So first of all I should say *SPOILERS* for the Ark of Lost Souls scenario and for any Mortis Thule mission

I'm currently coming to the end of running the Ark of Lost Souls scenario(s) and the Kill-Team will soon be escaping onto the surface of Karlack. I'm sure one of the PCs are going to want to return to Mortis Thule to complete one of the optional missions that they couldn't get to (the enslavers). This is because I seeded it with loads of stuff that would be interesting for his character (a lost member of his chapter with a rosarius from his parent chapter, potentially near by).

It would be just a bit boring for me to simply run that on it's own. By the time I get them back to this mission they will be rank 5 or 6, so I'll be wanting them to achieve something epic. The vague plan will be for them to be intercepted by an Eldar farseer that they met before, who will task them with going to the centre of Mortis Thule and disabling it. Of course I'll have to do something to ensure they don't simply kill the farseer, as they just might do, but that's outside the topic for this thread.

The Ark of Lost Souls book implies that in the centre of Mortis Thule is a Necron artefact that is creating the black rock substance of the space hulk. It doesn't however, give any notes on what it would look like, what size it is or any form of scale.

So my main questions are:

1/ Is there official information on what is at the centre of Mortis Thule anywhere outside the "Ark of Lost Souls" book?

2/ Has anyone else had PCs journey to the centre of Mortis Thule in their games? If so what did they find there?

3/ I always appreciate general suggestions. Anyone have any?

1/ Is there official information on what is at the centre of Mortis Thule anywhere outside the "Ark of Lost Souls" book?

The Achilus Assault splatbook has a few pages on Mortis Thule (pp. 61-66.) which might be worth to read, but as it pre-dates AoLS, the information it contains is even more vague - it only mentions a possible connection with the technology of the Warp Gate, and the Omega Vault's special interest. Also, when dealing with the Farseer, don't forget the best item in Table 5-2: Renown Penalties in RoB (p. 202.)

Action : The Battle-Brother makes an alliance with xenos, even if he later kills them / Renown Reduction: –2: This applies even if the alliance was ordered upon the Kill-team by their commanders

Awesome thanks.

I have been looking for that section in RoB, as they have already had to negotiate with the same Eldar farseer to not get trapped in a warp infused section of the Space Hulk.

3/ I always appreciate general suggestions. Anyone have any?

Whatever is inside, you could always to a twist like in the BL novel Death of Integrity (obligatory *spoiler alert* - also, read it, it's one of the better Space Marine Battles books), where there's an intelligent Dark Age of Technology ship in the centre which actively manipulates events to get out.

Well I need it to be Necron based, although I could do a bait and switch thing... Considering I'm not going to have a chance to read Death of Integrity Do you mind spoiling some more seeds?

Sure thing. I'm in a bit of a hurry, so here's the tl;dr version:

For the plot hook to work, the thing in the centre needs to have at least a rudimentary self-awareness, or be controlled by some kind of intelligence - it might be of any origin, Necrons included. In the novel, a Space Hulk always pops up around star systems of the same class, dispensing Genestealers wherever it goes and has an unpredictable movement pattern not tied to warp currents. At the end it is unveiled that the same type of stars are needed for the ship to collect fuel (in this case to leave the galaxy, but it might have any number of other nefarious reasons), and the 'stealers, while hated, were kept to bring the hulk to the attention of the Imperium, so that while trying to destroy it, the ship in the centre could be set free.

This is a variation of a basic and age-old plot: the party working very hard to reach the centre and possibly loot it or destroy it, but all of their actions are anticipated, or even planned for, by the entity in the middle (clues can be dropped, and the big bad might even directly influence some events on the hulk), and the Kill-Team's success means actually unleashing something much worse than a space hulk on the universe. How's it?

Thanks man!

Oh, I forgot one more thing (to drive the point home even more pronouncedly) - in the novel, the ship tricked (and, in the endgame, kind of forced) the protagonists to fix some broken subsystems in it - it was secondary generators, IIRC. If the thing inside Mortis Thule could pull off something similar, that would be both delicious (for you) and devastating (for the players)

It could expel all Necron ships from within while in an important place. Allowing them to get to their own tasks.

To put the last nail in the spoiler coffin, how did the marines overcome this in the story?

They didn't. After the AI ship took over their armour systems and mechanical components, and they suffered casualties from turned AdMech servitors and Genestealers, they finally managed to do an emergency teleport to get out in the very last second due to an unlikely intervention (the ship blocks the teleport signal, but a Black Rage-affected guy crashes in, and they're released long enough to get outside and get a lock on the homer), but the ship, with its systems now repaired, managed to escape before they could destroy it along with the hulk. Utilising this story arch in Deathwatch, of course, sets the team up for failure, so that later they can rectify it and slay the dragon they unleashed, so to speak.

The novel ran with multiple parallel story arches, one about the Blood Drinkers and the Curse, and one about the Novamarines First Company Captain, culminating in a huge Space Hulk cleanup operation with almost two hundred Terminators of the two Chapters deployed, so of course the scale needs to be adjusted. The usual AdMech "Oooohh, shiny, let's disregard all warning signs and bring mortal danger to everyone involved to get it" storyline is thrown in for good measure, but it's usually working in the setting, however cliché it may be (although it probably needs to be added that the Chapters were also bribed with a Strike Cruiser each). Anyway, these events take up about one chapter towards the end from the 23 or 24 in the book, so this info is about all - I hope it can provide some inspiration for your game.

I'll definatly be using a lot of this. Thanks a million!