So - I've spent the morning searching the forums and getting tips on things, but have gotten no reassurance yet that I can pull this off yet, or any idea on how to truly start dreaming up the idea.

A quick background on me: I've been playing with my gaming group for about 4-5 years now. I totally <3 them! My GM is probably the best I've ever seen and on three occasions now, he's talked me into a system, world or setting I was reluctant to try… only to have me fall so in love with it that am contributing background stories, legends, rumors and whipping up websites and forums for our games. This in turn has given him the idea that he'd really like me to try RUNNING a game… I suppose it makes sense. For as much as I can dream up on characters and extra tidbits, I can see the connection he'd make on wondering how I'd do at GM'ing. Plus - he so wants a chance to /play/ every once in a while. Over the last year, we've been playing Deathwatch and Rogue Trader, the latter of which I have been absolutely addicted to, so I want to keep the general setting the same since it is what I am most currently involved with.

The idea of Only War was brought up - but I am more interested in investigations and character-driven story components than a setting made primarily for … well Only War. Dark Heresy was my first choice - but in reading the suggestion of taking existing adventures to use for a first time GM --- well I can't. My GM has all of them and has read all of them. I know I could weave in a lot of detailed stuff to mess(ahem I meant interact) with the characters on personal/bg related things - but I am totally stumped on how to come up with an overall plot or agenda. This past year was my first delving into the WH40K universe, so I've picked up bits of lore but am nowhere NEAR solid on it. My GM is a good guy, and the rest of the players have promised to behave for me if I attempt this (hee, and they chivalry is dead!) so I know I'll get some help -- but admittedly, being used to his games, I feel so very very small trying to come up with something here.

What might you suggest for a good, simple, but interesting idea to get me started.

In defense of Only War, character interaction is entirely possible (assuming all players are interested in playing soldiers). Obviously, investigation is a bit more difficult, but at least on a smaller scale "we need your squad to go to this facility and check in with the guards," and basically turn it into the entire plot of Aliens is entirely possible. Yes, it lacks the longer term investigation aspects, but with some tweaking that could still come about (heck, the squad could be recruited as acolytes to an inquisitor mid-game; keep the advancement scheme of OW, but use the investigation side of DH).

OW works really well for a DH style game. Just swap out logistics for profit factor from rogue trader(starting PF of 5-10) and you should get the right feel for starting acolytes. I'm currently 9 weeks into my game and everything is running smoothly.

If your GM has the books I recommend taking a look at both the creature anathema and diciples of the dark gods. Creatures Anathema has adventure hooks following each creature entry and Disciples of the Dark Gods has so many plot and adventure ideas built right into the all the different faction descriptions that it's kind of hard not coming up with something.

I'd also consider pulling set pieces from various adventures and swapping out the the individual plots and finding a new way to string them together. For example the players are sent in to raid a nobles estate, that leads them to try and find a specific individual in the underhive, that causes them to travel to a void station to attend a meating between rogue traders, which causes them to ….. You get the idea.

If you have a couple favorite plots from movies or books consider mixing and matching the events in each so your players can't guess what's going to happen next in case they've seen that movie/read that book.

Bottom line is the first time you GM it's kind of scary. The more you do it however the better you get. My best advice is know the system your running pretty thoroughly and prep as much as you can. I don't mean prep a lot of material but make sure you know the material you're running for that session backwards and forwards. Write general notes on where you're trying to take the plot and track what the players have found out and what they're still missing.

Basically just don't worry about it so much and just do it. Even if it's not very good your friends won't hate you for it. Just make sure to ask after each session about things they liked and things they didn't like and any advice they have for what you can do better next time.

The fear of GM'ing for the first time is usually exaggerated. I can almost promise you that you will have a lot of fun and if you have people you trust as players nothing can go wrong even if everything goes wrong.

First, as I'm sure you know since you have been a player for a while, a player never does what you want them to do so don't bother writing/creating a too strict system. What I found the easiest when I started GM'ing was to try and make a closed area because it was easier to predict and control as a GM. My players absolutely loved that adventure and it's one of their favorites today.

Now this was for a fantasy game but this is what I did. My players were tasked to make characters on the wrong side of the law that had in some way been involved in a band of somewhat organized criminals. I should have had three players at the time but the third couldn't make it so I started with only two. They made two thieves.
The story behind the adventure was that a very good friend to the characters had left the organization a year or two before that and moved north because of a woman. He then sends them a letter inviting them to a wedding, and they of course travel to the valley up north where he is living. Their friend is now running a tavern in the village. When they get there their friend are missing and his wife seem reluctant to talk. The inquisition is in town to investigate witchcraft and a curfew is in place. Some villagers are reluctant to talk and afraid, others seem haunted or burdened. Then the snow came and the village was cut off from the rest of the world for a whole winter. There was no way to get across the mountains so the players had to get on top of what was happening.

The background story was that the village had some left over residue from an old and long since dead culture. They worshiped animals to the degree that they tried to merge themself with them with… magic (no not furries I promise). Something went horribly wrong when they finally succeeded to merge a human with an animal and it started a plague of mutations where everyone who touched an animal merged with it and they became horribly disfigured and disgusting. Those that survived like for a few years built a burialchamber deep under the village and stored their corpses there incased in ice. The people who later settled there to do mining in the mountains suffered great losses in the same mutation but soon gained resistance.

Recently the guard force which suspiciously enough is quite large for such a little village started to mutate into wolf looking beasts (werewolfs) once bitten by a wolf from a huge pack that had been terrorizing the village recently. The wolfs has nothing to do with that old civilization, it's the wife of their friend together with two others, that opposes what has happened in the village, who has stolen the pups of the wolfs and put a form of curse on them to attack the mayors men. So I had two big secrets in this valley.

The plus side to this is that you have an enclosed space which you can draw up in quite close detail. I sketched out the village, all the surrounding farms, then I created the people who lived in each house and roughly how they were related. Put in secrets in almost every house so no matter where the players went there would be something strange happening or something to find. This ensured that the game never came to a standstill and I never lost control because the players went to an unchartered area. I could have such detail in every character the player met and have so much prepared without tying the players hands because within the valley they had total freedom and I never interfered with anything.

If you want to use any of this. Go crazy and make a kickass adventure. I hope you found something of use from all this text. If only the story of how someone else solved that scary first time. ^^

Get Disciples of the Dark Gods and read through the various factions there, lots of interesting opponents. Set up some small time cult cell somewhere remote and spend some time building the environment up. In the first game the players need to find the personality of their characters, and it is great to have a local environment where they can interact with some npcs to "introduce" their character to the other players. An early bar brawl or not too dangerous skirmish is good fun to start on too.

Don't go for a long story plot before you know your characters. After 6 or 7 sessions I started on the Harlock trilogy and I changed it a lot to fit with the players - especially I rewrote most of Damned City to be located back in their starting town, which was great fun as they could revisit some of the early npc's they had been interacting with.