Setting: A research base at the bottom of the Marianas Trench
Depth: 10,000 meters.
Mission Duration: Thirty days
Note: This is a follow-up to my previous question: What would drive people to risk death in the deep?
A research base lies at the bottom of the Marianas Trench, housing 10-12 scientists of both sexes and a cat.
This tightly knit team has been hand-picked and intensively trained for a high-risk mission that cannot and must not fail. After a series of deep sea missions, they will be sent to Jupiter in order to replicate these missions in the depths of the seas of Europa, where the only other life in the solar system might exist.
Each of the crew members has gone through rigorous psychological profiling, testing, and any possible genetic markers of mis-content have been genetically sliced away.
These guys are the cream of the crop, the best of the best for this mission.
However, one by one, they start to die, and it becomes obvious that their deaths are not accidental.
What possible reason could cause one (or more) team members to kill the others that would not be anticipated by the training they've undergone?