[Michael Cule]

It's a covert and unauthorised bio-warfare research lab.

It's been developing a disease that will either kill or de-power psionically gifted people. (Probably a bit of both: you can't affect a core part of the nervous system without a certain risk of death.)

The employers could be the Zhodani but they would come in with their own psychically gifted commandoes and that would be effective but dull.

So let's make the employers a faction of the Imperial services who do not approve of this sort of thing. And let's make one of the PCs (only) a member of the Emperor's small group of elite and trusted psionic agents. And let's make at least one of the mercs that have been hired to do the job extremely psi-phobic.