Having just found out that some of my friends are in a Dark Heresy group, I've been toying with the idea of running a sort of hybrid game.

I'd collaborate with the GM for their DH games to create a campaign that both groups will play, simply from their own perspective. We'd plan between each session according to what the other group has done. Our Explorers will be affected by the actions of their Acolytes, and vice versa. At times, players from one group may temporarily go with the other, and maybe at some point we'll attempt a joint game (but that might be a lot of people).

Anyhow, any suggestions? Think it will work?

Dark Heresy tends to be on a smaller scale than Rogue Trader does. Acolytes rarely have the option of nuking the site from orbit, for example. It makes it difficult to have an equal level of influence between each group, unless the Acolytes have made it to Ascension and become proper Throne Agents. What you could do is have occasional overlap between the two. Say, the Explorers are forced to go back into the Imperium to have their flagship refitted at the Lathes or somesuch. While they await the repairs, the Acolyte's Inquisitor requests the use of one of their secondary vessels as a transport. Both groups overlap when a string of murders occurs aboard ship while the ship's in the warp; for the Acolytes it's their duty to root out the cause before the murderous ritual is completed, while for the Explorers it's a desperate race to remain in control of their own vessel. Keep in mind that a Rogue Trader's authority, the place they belong, takes place only outside the borders of the Imperium. Most Acolyte cells act within the borders of the Imperium, though obviously that depends on the proclivities of their Inquisitor.

It can work every now and then as a diversion, but I wouldn't make it a regular fixture.

It's certainly a tempting idea. I've thought about doing similar things myself, but never actually done them.

There are two major problems I can foresee:

1) Two GMs. You might not always agree on which direction you want the story to go, and that could cause problems for both groups. What one GM is willing to allow, the other might not. This is especially problematic if the question of "can I do this?" gets raised in the middle of one session, when no one from the other is around to say anything. There's an extra red flag on this issue since it sounds like the other GM has been running his game for a while now. He's already in a groove and might not enjoy it if your ideas buck the wagon.

2) Timing of character actions. If both groups are on the same planet at the same time (or otherwise in close proximity) they might bump into each other. How do you handle that? Stop the game and prepare a giant "merged session" for sometime in the coming week? That's probably the best way to handle it from a mechanics point of view, though it might be a logistical nightmare. The other option is to have the GM of the game in progress start NPCing the players from the other game. I shouldn't need to illustrate all the ways that can go wrong.

As far as advice to make this idea work, I would suggest two things:

1) Start two new games instead of trying to tack one new game onto a long-running campaign. That way both games can grow in each otehr's presence instead of one invading the other's established paradigm.

2) Separate players from characters. If you're not famailar with the West Marches experiment, I suggest you look it up (just do a google search, it's out there.) Basically, have a pool of characters, perhaps pregenerated, and let each player pick a character each session - not necessarily the same one, but if they develop favourites that's fine. This is important because it disassociates the player from one single character. If that character, even a favourite, ends up dying in a session the player wasn't around for, he's less likely to be upset about it since no one had fixed characters anyway. This will also give the GMs a certain amount of leeway for what they want to do in their own sessions, although it will require an even stronger agreement about what kinds of class/gear/race options should be allowed, since something one GM allows might end up infiltrating the other game more easily this way.