Actually no, they do not outrank the Chapter Masters of the Adeptus Astartes or anything else in that list really. The Holy Ordos were founded by Malcador the Sigilite to police and oversee the Imperial Adeptus. They do not however have purview over their actions unless they may prove that those are opposed to the Imperium.

The figures you mentioned cannot be ordered save from the Emperor himself, that and the High Lords that act as his voice. An Inquisitor has great power yes, but even that has limits. Go pissing off a Lord Admiral or a Sector Governor and you can find yourself isolated from your peers. Piss off a Chapter Master or a High Fabricator and you can find yourself dead.

Depends. Space Marine chapters are set aside from the rest of the Imperium but the Emperor set up the Inqusition to be his left hand and in the backgound it mentions that Inquisitors are...

'the only individual that is exempt from its scrutiny is the Emperor himself. If he has good cause, an Inquisitor may demand any service from any Imperial citizen, up to and including the High Lords of Terra. The Adeptus Custodes who guard the Emperor's palace and person are exempt from conscription, because their duty to the Emperor is clear and unchanging'

As to the Space Marines...

'When it comes to the Adeptus Astartes, Inquisitors often show some discretion, as Space Marine Chapters are often willing to come to blood over any infringement on their Emperor-granted autonomy. However, not even the Adeptus Astartes are immune from the Inquisition's scrutiny and justice, and entire worlds have been destroyed in order to cleanse them if they were deemed traitorous.'

Agreed. But the problem is convincing people of the 'good cause' - the Imperium doesn't have battlefleets and armies standing idle, so any resources an Inquisitor wants to pull in to do something isn't doing something else , the consequences of which could be just as bad - or at least clearer and more immediately urgent, since the Inquisition is often loathe to explain precisely what it wants those resources for .

Agreed. But the problem is convincing people of the 'good cause' - the Imperium doesn't have battlefleets and armies standing idle, so any resources an Inquisitor wants to pull in to do something isn't doing something else , the consequences of which could be just as bad - or at least clearer and more immediately urgent, since the Inquisition is often loathe to explain precisely what it wants those resources for .

It's less about convincing people of the 'good cause' and more the scrutiny it brings from other Inquisitors. If your Inquisitor borrows resources that are needed elsewhere then he better have a **** good reason as he might have to go before a conclave and explain exactly why he needed that battlefleet. An Inquisitor has the power to call down an Exterminatus but, at some point, he's going to have to stand before his peers and justify his actions (and he better have plenty of evidence as to why everybody on the planet needed to die). Even Inquisitor Kryptman wasn't immune to scrutiny after he set up the Galactic Cordon against Hive fleet Leviathan.

To get back to the OP's questions...

Thanks for all the answers so far!

If you don't mind, here are four things I'd like to ask for your help with:

1. Specific scenario starters. I mean, if I was writing a Call of Cthulhu scenario, it'd probably open with a murder But, would a single murder get an attention of an Inquisitor a few star systems away? If not, then... what matters would the Inquisitors investigate?

They can investigate whatever they want - they have almost complete autonomy. If they think a planet's governor is corrupt, they'll look into them. More likely, however, is sending rookie agents to look into what may or may not be a matter for the Inquisition to care about. Murders can be garden variety or indicative of heretical activity. Any heretical organization is going to need material and resources, so odd paperwork or unlisted ship cargo might be a matter for investigation. Even local folklore, social unrest, or mass panics might point to something darker. Pick something you'd like to run as the GM and roll with it.

To use an example from my own games, I had the players land in a hive they'd never been to, meet at a pre-arranged safehouse to receive their orders: here's a name and a face, find and kill him. All of the cool plot and details evolved from that setup. (He was a terrorist, and later they learned he was a radical inquisitor operating with his cell in this hive)

2. Assuming that the Inquisitor has informants on some planet - how would such informants pass any info to him / her? I mean, going to an Astropath isn't really safe - wouldn't an Astropath start babbling around, if made to send a message to an Inquisitor?

Astropaths work for the Imperial apparatus and are valued for their discretion. You can also have them transmit encrypted information, so what they even see is basically garbage. You might want to research Cold War era spycraft. Full of useful spy bits for things like this.

3. In what ways do the Acolytes investigate stuff, exactly? Let's say they are sent to investigate a murder - how should they approach it? The trail would be at least weeks old, there would no crime scene, the witnesses would be hard to track down... So, what is there for the Acolytes to do?

This is kind of up to them. As the GM, your job is to present the players with a problem and clues. It's up to them to figure out how to solve it and how the clues fit together.

A trick I picked up is this: let your players tell you what's happening in the plot. Create a bunch of small, seemingly unrelated clues, and the players, invariably, will come up with a cooler story that fits them together than you would have. Probably multiple. Pick the coolest and that's what happened.

In the case of your specific example, unless it was on a backwater planet, someone investigated it. Point the PCs to them.

4. What kind of people are recruited as Acolytes? I might be introducing the game to people new to DH and WH40K in general. So, how do I tell them what kind of characters they need to create? And, overall, what does it take for a character to get noticed by an Inquisitor - they aren't drafting random soldiers or scribes, aren't they..?

Basically anyone. Individual Inquisitors can basically recruit whoever they want without much in the way of oversight, even out from under military commanders or other high ranking people (there would be a social cost, obviously). Have them create the kind of character they will want to play and when everyone is finished, figure out why each one was recruited (your players can just tell you) and how the group works together, or if this is their first mission together.

Agreed. But the problem is convincing people of the 'good cause' - the Imperium doesn't have battlefleets and armies standing idle, so any resources an Inquisitor wants to pull in to do something isn't doing something else , the consequences of which could be just as bad - or at least clearer and more immediately urgent, since the Inquisition is often loathe to explain precisely what it wants those resources for .

It's less about convincing people of the 'good cause' and more the scrutiny it brings from other Inquisitors. If your Inquisitor borrows resources that are needed elsewhere then he better have a **** good reason as he might have to go before a conclave and explain exactly why he needed that battlefleet. An Inquisitor has the power to call down an Exterminatus but, at some point, he's going to have to stand before his peers and justify his actions (and he better have plenty of evidence as to why everybody on the planet needed to die). Even Inquisitor Kryptman wasn't immune to scrutiny after he set up the Galactic Cordon against Hive fleet Leviathan.

Please don't take this the wrong way but your views on the absolute authority of an inquisitor sound naive to me. While de jure , inquisitors wield a lot of authority, de facto they are limited when it comes to dealing with equally powerful officials. Nobody operates in a (political) vacuum so there are always competing pressures involved. As you portray it, all the inquisitor need worry about is justifying his actions afterwards.

I think an inquisitor would be hard pressed to even get what he wants if it goes beyond a few hundred men or a void ship. Because that upsets other (routine) plans made by equally powerful people.

Let's say an inquistor wants the use of a battlefleet. The admiral says no. What is the inquisitor going to do to make him?

He can't physically threaten him....he be thrown out of a void-lock. He can't kill him, the admiral will have too many bodyguards around (if he's smart). Most likely, the inquisitor will throw a temper tantrum and go home to mommy and complain that the admiral was being mean to him. And get the conclave to help sanction the admiral.

Now let's assume that admiral was under orders. From his sector superiors. Who were acting under orders/in cooperation with another inquisitor. Perhaps an inquisitor with more prestige/influence/rank. Your inquisitor's whining will be ignored as the admiral did nothing wrong.

In fact, any peer of the imperium worth his salth will likely have cultivated several inquisitors and have woven a web of favours and debts which can be called in whenever an uppity inquisitor comes calling. "What's that you say? You want to commandeer my entire PDF? I would be happy to comply with your totally lawful decree but unfortunately, this other inquisitor ordered me to hold my PDF in reserve until I hear from him. I respectfully suggest you work this out amongst yourselves...."

And even when complying, there is a world of difference between cheerful and willing compliance and dragging your feet bureacratically. Especially in a dysfunctional Imperium where switching on the light requires an hour of chanting...

I am a minor official and have learned that not all department heads are created equal. Some of them have enough influence to be practically inviolate to any audit due to political connections.

WH40K is nothing if not a setting in which competing feudal factions compete. The inquisition is but one of them. Anyone not playing the game properly is easily removed. Just as in real life politics. A newly minted inquisitor demanding the entire sector fleet from the Lord Sector without providing any reason/evidence of a sector wide threat will not get it IMO. Simply because the Lord Sector has his own responsibilities and can't justify leaving entire systems undefended.

What the newly minted inquistor should have done is presented his reasons to his peers and get consensus that a sector wide threat is emininent after which the inquisition informs the Lord Sector that the sector fleet is required....Hence the influence system in game and the cautionary words in the core book about influence....

Agreed. But the problem is convincing people of the 'good cause' - the Imperium doesn't have battlefleets and armies standing idle, so any resources an Inquisitor wants to pull in to do something isn't doing something else , the consequences of which could be just as bad - or at least clearer and more immediately urgent, since the Inquisition is often loathe to explain precisely what it wants those resources for .

It's less about convincing people of the 'good cause' and more the scrutiny it brings from other Inquisitors. If your Inquisitor borrows resources that are needed elsewhere then he better have a **** good reason as he might have to go before a conclave and explain exactly why he needed that battlefleet. An Inquisitor has the power to call down an Exterminatus but, at some point, he's going to have to stand before his peers and justify his actions (and he better have plenty of evidence as to why everybody on the planet needed to die). Even Inquisitor Kryptman wasn't immune to scrutiny after he set up the Galactic Cordon against Hive fleet Leviathan.

Please don't take this the wrong way but your views on the absolute authority of an inquisitor sound naive to me. While de jure , inquisitors wield a lot of authority, de facto they are limited when it comes to dealing with equally powerful officials. Nobody operates in a (political) vacuum so there are always competing pressures involved. As you portray it, all the inquisitor need worry about is justifying his actions afterwards.

I think an inquisitor would be hard pressed to even get what he wants if it goes beyond a few hundred men or a void ship. Because that upsets other (routine) plans made by equally powerful people.

Let's say an inquistor wants the use of a battlefleet. The admiral says no. What is the inquisitor going to do to make him?

He can't physically threaten him....he be thrown out of a void-lock. He can't kill him, the admiral will have too many bodyguards around (if he's smart). Most likely, the inquisitor will throw a temper tantrum and go home to mommy and complain that the admiral was being mean to him. And get the conclave to help sanction the admiral.

Now let's assume that admiral was under orders. From his sector superiors. Who were acting under orders/in cooperation with another inquisitor. Perhaps an inquisitor with more prestige/influence/rank. Your inquisitor's whining will be ignored as the admiral did nothing wrong.

In fact, any peer of the imperium worth his salth will likely have cultivated several inquisitors and have woven a web of favours and debts which can be called in whenever an uppity inquisitor comes calling. "What's that you say? You want to commandeer my entire PDF? I would be happy to comply with your totally lawful decree but unfortunately, this other inquisitor ordered me to hold my PDF in reserve until I hear from him. I respectfully suggest you work this out amongst yourselves...."

And even when complying, there is a world of difference between cheerful and willing compliance and dragging your feet bureacratically. Especially in a dysfunctional Imperium where switching on the light requires an hour of chanting...

I am a minor official and have learned that not all department heads are created equal. Some of them have enough influence to be practically inviolate to any audit due to political connections.

WH40K is nothing if not a setting in which competing feudal factions compete. The inquisition is but one of them. Anyone not playing the game properly is easily removed. Just as in real life politics. A newly minted inquisitor demanding the entire sector fleet from the Lord Sector without providing any reason/evidence of a sector wide threat will not get it IMO. Simply because the Lord Sector has his own responsibilities and can't justify leaving entire systems undefended.

What the newly minted inquistor should have done is presented his reasons to his peers and get consensus that a sector wide threat is emininent after which the inquisition informs the Lord Sector that the sector fleet is required....Hence the influence system in game and the cautionary words in the core book about influence....

Don't worry I'm not really that concerned as there are plenty of different views on the 40K universe. I look at the background of the Inquisiton and see an organisation that is beholden to no one except the Emperor and who speaks with his voice. That's a pretty big thing in a society which worships the Emperor as a god and heresy is pretty much the worst offence that anybody can commit. When Inqusitors speak other people are expected to listen. I'm also not saying that Inquisitors don't politic. Kryptman, for example, had to forge a massive alliance between Space Marine chapters, Imperial Guard commanders, Battlefleet admirals, Planetary Governers and Sector Lords in order to combat the Tyranids and he didn't do it just on the basis of ordering people around.

The question you have to ask yourself in the case of the 'Inquisitor requesing a battlefleet' example is what scale of crisis has led him to step onto the bridge of the flagship of an Imperial Navy Fleet and order the Admiral to do something. If the Admiral says no do you really think that's a situation that the Inquisitor can just 'go home to mommy'?

The question you have to ask yourself in the case of the 'Inquisitor requesing a battlefleet' example is what scale of crisis has led him to step onto the bridge of the flagship of an Imperial Navy Fleet and order the Admiral to do something. If the Admiral says no do you really think that's a situation that the Inquisitor can just 'go home to mommy'?

I'd argue that this situation proves my point (to some extent ).

It won't be a newly minted inquisitor who unearthes a sector wide threat requiring a battle fleet to resolve it. That will be an older, more established inquisitor who will built up the influence to get the assistance of those assets required to get the job done over a long career. After all, a new inquisitor needs to build up his assets first, create teams of acolytes, safe houses, funds etc....

And I wouldn't get to hung up on the notion that they represent the Emperor and thus speak with his voice etc. The higher up you get, the more jaded people get. The high council on Terra is more preoccupied with maintaining or enlarging their power than speaking for the emperor and defending the Imperium. That's just fiction they spout to get simpler minded peons to obey. In medieval times, the kings were chosen by god etc. but still had great difficulty getting their vassals to do what they wanted them to do. Granted, young inquisitors are likely zealots who actually believe the whole left hand of the emperor but zealots often fare poorly......they certainly have difficulty getting things done...

The question you have to ask yourself in the case of the 'Inquisitor requesing a battlefleet' example is what scale of crisis has led him to step onto the bridge of the flagship of an Imperial Navy Fleet and order the Admiral to do something. If the Admiral says no do you really think that's a situation that the Inquisitor can just 'go home to mommy'?

I'd argue that this situation proves my point (to some extent ).

It won't be a newly minted inquisitor who unearthes a sector wide threat requiring a battle fleet to resolve it. That will be an older, more established inquisitor who will built up the influence to get the assistance of those assets required to get the job done over a long career. After all, a new inquisitor needs to build up his assets first, create teams of acolytes, safe houses, funds etc....

And I wouldn't get to hung up on the notion that they represent the Emperor and thus speak with his voice etc. The higher up you get, the more jaded people get. The high council on Terra is more preoccupied with maintaining or enlarging their power than speaking for the emperor and defending the Imperium. That's just fiction they spout to get simpler minded peons to obey. In medieval times, the kings were chosen by god etc. but still had great difficulty getting their vassals to do what they wanted them to do. Granted, young inquisitors are likely zealots who actually believe the whole left hand of the emperor but zealots often fare poorly......they certainly have difficulty getting things done...

I don't feel it proves much as I'm not sure exactly when we suddenly started discussing 'new' Inquisitors versus older ones. I honestly don't think I've ever mentioned this in any of my previous posts. Even if we are discussing a 'fresh out of the acadamy' Inquisitor what's to say that he does come across something? Maybe he's the only Ordo Malleus Inquisitor in the sector? Maybe he's from one of the lesser Ordos? Maybe he happens to be in the right place at the right time? Maybe he takes over an investigation left to him by his mentor?

I find your take on the Imperium a bit depressing TBH; one where Inquisitor Lords and the High Lords of Terra just sit around defending/maintaining their power base. I look at the background of Inquisitors like Kryptman, Coteaz, Czevak, Darkhammer, Eisenhorn, Vail etc and I don't really get that impression from any of the writing that GW has done for them. Heck the 40K universe is full of zealots; the whole Imperium is built on the worship of the Emperor as a God.

The question you have to ask yourself in the case of the 'Inquisitor requesing a battlefleet' example is what scale of crisis has led him to step onto the bridge of the flagship of an Imperial Navy Fleet and order the Admiral to do something. If the Admiral says no do you really think that's a situation that the Inquisitor can just 'go home to mommy'?

The fact that the Inquisitor actually need sais ressources means he doesn't have them, so he can't force said admiral into giving him said ressources. So if the Admiral says no, he only have force (physical, psychic or else) to try to force him, which the Admiral will answer to in at least equal or even superior order. And your said Inquisitor, if he's bright, won't draw a plasma pistol to threathen an Admiral to his bidding while he has 30 elite naval bodyguards in full armours with great gear and such.

So the Inquisitor will be either dead, or running to his peers to ask for support. Maybe they will listen to him, but it is also possible that the entire battlefleet is fighting a Waaagh or a Hive Fleet or an eldar incursions, and can't be called to act against this esoterical threat the Inquisitor speak about and he will have to use other ressources to succeed.

I find your take on the Imperium a bit depressing TBH; one where Inquisitor Lords and the High Lords of Terra just sit around defending/maintaining their power base.

Depressing but exactly in line with the fluff GW and FFG depicts. The Imperium is corrupted to personnal interests or worse (xenos/chaos corruption) and isn't a shinning example of virtue. Yeah, there are people who does. These are the main characters of stories we hear about.

But read Eisenhorn; look how much many Inquisitors are as*holes, look how many politicians, nobles and officials of the Empire are as*holes. Look how much he must sift through politics to be sure his authority is recognised and to be sure that he succeeds in his cases.

Go read Ravenor, and see the same problem. Go read Pariah, see the same problem.

Go read Atlas Infernal, with Czevak, and see that the same problem is there.

The fact is, even a police officer with proofs and the backing of the law won't get far if his ennemies have judges, courts and officials in their pocket. See how the international court of justice on our heart is supposed to have great powers but in fact, could never put behind bars an american president even if he did real crimes (and we have some recent cases).

The higher the powers, the greater the problems to their applications.

What I've always told my players is this:

In theory, you have absolute authority to do whatever the heck you want.

Meanwhile, back in real world, you have exactly as much authority as the people you deal with chose to give you.

I find your take on the Imperium a bit depressing TBH; one where Inquisitor Lords and the High Lords of Terra just sit around defending/maintaining their power base.

Depressing but exactly in line with the fluff GW and FFG depicts.

It's odd because I keep reading stuff like this...

In the modern 41st Millennium, the Inquisition is the most powerful organisation of the Imperium's many branches. Its agents, the Inquisitors, command fear and respect in equal measure. They are creatures of myth as much of flesh and blood, relentless beings who descend from on high to pass judgement upon the mutant, the traitor and the heretic. It is a rare citizen who does not dread drawing an Inquisitor's steely gaze, who does not experience the starkest terror in his or her presence. Every Imperial citizen, from the poorest of underhive scum to the highest and wealthiest of nobles, has heard the tales of death and destruction, of the all-seeing eye that condemns or absolves with impunity. Those who have crossed an Inquisitor's path and survived to tell of it are seldom eager to invite his attention again.

and this...

Inquisitors themselves care little for morality, and nothing at all for the Imperium's many laws and procedures, except when they choose to make use of them. They are the Emperor's left hand as the Adeptus Terra is his right, and stand in judgement over all the Imperium's organisations. Indeed, an Inquisitor is apart from the rest of Mankind in every way that matters. By ancient tradition, his authority comes directly from the Emperor himself; there is no hierarchy to which he must answer, and he is beholden only to his fellows. More than this, a bearer of the Inquisitorial Seal can requisition any servant in the Imperium to assist in his mission, from the lowliest of clerks to entire Space Marine Chapters and Imperial Navy battlefleets.

and this...

The Inquisition is immensely powerful, and the only individual that is exempt from its scrutiny is the Emperor himself. If he has good cause, an Inquisitor may demand any service from any Imperial citizen, up to and including the High Lords of Terra. The Adeptus Custodes who guard the Emperor's palace and person are exempt from conscription, because their duty to the Emperor is clear and unchanging. When it comes to the Adeptus Astartes, Inquisitors often show some discretion, as Space Marine Chapters are often willing to come to blood over any infringement on their Emperor-granted autonomy. However, not even the Adeptus Astartes are immune from the Inquisition's scrutiny and justice, and entire worlds have been destroyed in order to cleanse them if they were deemed traitorous.

The Inquisition needs to politic according to this....

In practice, the Inquisition must be more political than its mandate allows. Though their power derives from the Emperor himself, and even the High Lords of Terra are not above their scrutiny, the Inquisition must also rely on the other parts of the Imperium for resources. The Inquisition has tremendous amounts of power, and has access to troops, weaponry and archives beyond most other Imperial organisations, it must still receive these from the Adeptus Astartes, the Imperial Guard, the Adeptus Mechanicus and others

and their power isn't limitless...

The Inquisition’s remit places it above all of the Imperium’s institutions, with the exception of the Senatorum Imperialis— the High Lords of Terra themselves....An Inquisitor would be foolish indeed to arrive at a world suspected of imminent secession and attempt to arrest the Imperial Commander, for he may find the entire population rising in opposition. Therefore, an Inquisitor in such a position has to ensure that there are significant resources at hand to combat an uprising, and to attain them he has to gain the support of other bodies.

In practice then, Inquisitors are essentially ‘peers of the Imperium.’ Although many consider themselves answerable only to the High Lords of Terra and the Emperor Himself, in reality there exists a class of high-echelon Imperial servants, to which Inquisitors belong, all who wield more or less the same levels of influence. Such worthies include Imperial Governors, Imperial Guard Generals, Space Marine Chapter Masters, Rogue Traders, Lord Admirals, Adeptus Arbites Judges, and the sector level representatives of the Administratum. Relations between these various groups are often seething with internecine rivalry and bitterness, and even within one grouping, deadly wars may be fought to gain influence and leverage. Imperial Commanders, for example, quite frequently engage in bitter and bloody territorial clashes, and the Inquisition is far from immune to internal strife.

but there's still plenty of this...

A follower of the Monodominant credo, Emil Darkhammer firmly believes that the Imperium's only hope of survival is for all other races in the galaxy to be destroyed. He has no tolerance for any deviation from the purest interpretations of Inquisitional lore. For him, there can be no shades of grey when it comes to interpreting the Emperor's word, only darkness and light. All Inquisitors are ruthless -– they must be to protect Mankind from threats both within and without – yet Darkhammer's uncompromising philosophy is harsher than most. It is a cornerstone of his methodology that nothing and no one can be ranked as indispensable in the cause of Mankind's survival. The Imperium must, after all, be kept safe at all costs -– no matter what the tally in lives or worlds might be. This belief has earned Darkhammer many detractors, not only within the ranks of the Inquisition, but in the wider Imperium as well. However, even the highest-ranking dignitaries are reluctant to disobey or criticise an Inquisitor, let alone act in opposition to him, so Darkhammer's actions meet with few obstructions.

I think I'll just leave it there as I'm pretty sure we're going round in circles. Sure the Admiral can tell the Inquisitor to **** off, why not. If he's lucky his bodyguard will agree to escort the Inquisitor off the bridge. If he's unlucky his bodyguard might decide that the Inquisitior has a point. I doubt that things would end well because if things were so desperate that the Inquisitor felt that the only way he could possibly succeed was with an Imperial battlefleet right now (weighed against what the fleet was already doing) then I don't think organising a meeting with other Inquisitors and using 'other resources' would really be on the cards.

Ultimately its worth remembering that the 'powerful organisation' blade cuts both ways.

You just quoted more than enough things that clearly states that an Inquisitor hasn't absolute powers.