So, my game isn't going to be set in the offical FFG setting, but in a sector of my on creation. That being said, I have been pondering making the Tau a major adversary. One of the ways I was thinking of doing this was a plot that was uncovered where Gene Seed was captured by the Tau, and they were going to experement with it and their Fire Caste. Of course, the Kill Team must rush to recover it and destroy all the research the Tau have on the Gene Seed.

I was also thinking of throwing some Kroot as enemies that have consumed Space Marines, so are mega awesome Kroot.

That's very creative. The question that would arise is why does the Deathwatch do this and not the Chapter(s) stolen from ?

Unless, of course, the chapters themselves are in fact after the thieves and the DW has a mission as yet unknown to the players ? Maybe that leads to some interesting confrontations - maybe the Ordo Xenos has an interest in seeing the the experimentation go through on a very limited scale and the characters are sent to counter some of the other Chapters' endeavours ?

Or maybe, something I have been speculating on, there is a larger problem with the Empire - maybe even with the Emperor himself - and the experimentation that the Tau will carry out are required to help mend/cure/augment the Emperor's Throne (of course that would be really really secret)....

Spin it on....

Considering how different Tau and Humans are biologically I'm not too comfortable with the idea that Astares geneseed could be used by Tau to create super-Tau... Kroot are another matter due to their capacity to assimilate new genetic material. And, of course, there is always the Gue'vesa human auxiliaries of Tau Empire so conceivably Tau could create their very own Space Marine auxiliaries... How wicked would that be?

As an answer to what Ariolan asked "why does Deathwatch do this?" I will suggest following:

The geneseed was not stolen from the chapter itself but is part of the chapter tithe of geneseed to Adeptus Mechanicus. Understandably the Inquisition and Adeptus Mechanicus do not want to reveal this to the chapter in question as such a leak could put doubt over the whole system of tithing geneseed to Adeptus Mechanicus and potentially cause a rebellion amongst the Astartes chapters already a bit suspicious of tithing their geneseed. Nobody wants a new Badab War, now do we?