**This wasn't getting much love in the RT forum, so I figured I would try here as well**
I need help coming up with the motivations of some Dark Eldar antagonists. Aside from the standard knowledge, I don't have a all the ins and outs of this race figured out. That's where you all come in. First, I will lay out the details of the game I am running.
Game: It is based on the Rogue Trader rules/Tau PC Guide but heavily modified; it uses the DH2/OW/BC combat system as well as skill/talent descriptions. On top of this, we are also working with a nice list of house rules and homebrew equipment/gear/weapons etc.
Story: PCs are part of an elite Tau task force which currently consists of two fire warriors and one gue'vesa as well as a number of optional NPC companions to accompany them on missions; the latter of which helps fill out tactical roles the small group may be missing out on. They operate similar to how a Deathwatch kill team might - rolling around in a frigate under the command of a Shas'el taking missions as they come along.
Currently in the story, they have just started their first mission. A series of pirating raids in a system on the edge of the third sphere expansion have resulted in a number of lost merchant ships and a hefty amount of cargo - specifically aid shipments to colonies on the outer rim. A merchant vessel filled with Tau Marines and gun drones was set as bait on the edge of the system with its distress beacon activated to lure the pirates in in classic Kauyon style. PCs set up at the edge of the system in their frigate with stealth fields activated. Sure enough, raider vessel entered the system after a few short days of waiting and took the bait. They have a series of objectives to complete - primary, secondary, and tertiary - with plenty of mishaps in the works by yours truly.
The PCs infiltrated the open hangar via modified Orca gunship with stealth fields activated. They are currently in the middle of rolling initiative for their first fight after their not-so-sneaky Tarellian berserker and Demiurg operator were heard sneaking into the hangar control room.
Anyways, that is all background info. Onto the meat and potatoes:
A Dark Eldar ship is going to transit into the system as well. I have a vague story of how the chaos reavers and the dark eldar are in league with one another - a mutually beneficial raiding relationship - that each is expecting to crumble anytime. But I want to have the dark eldar involvement mean more to the larger, overarching storyline. Not just a one off. What would the DE be doing in the system? Obviously something sneaky and more nefarious than simple raids. Are they seeking out a necron tomb world? Are they looking for some lost relic that they heard was in the system?
I want to have the Dark Eldar ship get the hell out of dodge when/if they become aware of the Tau mothership. But why? I am having trouble coming up with some ulterior motivation for these baddies.
Secondly, what type of ship would you recommend the Dark Eldar be roaming around in? I would imagine it is nothing larger than a frigate - more likely something smaller.
Thanks in advance. If you have any other questions for me, don't hesitate to ask.