Question: **Dateline**: 2067

**Setting**: A research base at the bottom of the [Marianas Trench](https://en.wikipedia.org/wiki/Mariana_Trench)

**Depth**: 10,000 meters.

**Mission Duration**: Thirty days

A research base lies at the bottom of the Marianas Trench, housing 10-12 scientists of both sexes and a cat.

The mission starts well, the team have trained together for months, and they're tight knit. At least they thought they were...

One by one, they start to die, and it becomes obvious that their deaths are not accidental.

**Question**:

What would be a reasonable prime purpose of this research mission? For what reason would a dozen scientists be sent to the bottom of the ocean for a month where a robot/scans would not be appropriate?

Answer: 
You could take inspiration from the game *Subnautica*. In the game, the player crash lands on an alien planet which is covered with water. While trying to survive, he learns that the aliens that used to live on the planet had been wiped out by a virulent disease. They had been researching various lifeforms on the planet in the hopes of finding one that was resistant to the disease, so that they could extract that resistance and save their species. Most of their research was done thousands of meters underwater, because that's where the most promising creatures lived.

In your situation, the scientists could be researching anything about the local fauna, as long as they need physical samples for their tests - anything from blood work to actual live specimens. Robots and scans might be able to determine general information about the creatures, but they would probably not be able to retrieve these samples without damaging them (after all, removing the samples from their natural high-pressure environment could cause some crucial piece of info being lost somehow), so the only logical conclusion is that research has to be done manually and on-site.
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> What would be a reasonable prime purpose of this research mission? For what reason would a dozen scientists be sent to the bottom of the ocean for a month where a robot/scans would not be appropriate? 
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**There is none,** robots are more effective at scientific data collection down there than humans so there is no value at sending humans. 

The premise of this plot is flawed conceptually. 30 days is way to short to acclimate to the pressure differences. Deep sea divers on oil rigs spend months in pressure chambers before and after their operational stint. It is also extremely risky where an accident can result in fatality or long term injury. Sending scientists is infeasible when scientists are better used analyzing data instead of doing dangerous hands on work. 

What would more likely be the case is you have a dozen technicians sent down there to maintain equipment and do detail work machines cant yet do. However, at these pressures the human body cannot be acclimated to survive without an external vehicle (like a futuristic mech dive suit). 

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> What physiological reason could there be for one (or two) members of the research team to kill others, but for that same cause not to affect any other member of the team?
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In these situations the common conditional occurrence is called "Cabin Fever". Essentially when a human trapped in a confined space with limited social exposure for long periods, certain predisposed minds can snap in violent and/or psychotic ways. This rarely happens in deep sea or space missions anymore as candidates usually undergo psych evaluations to prevent exactly this scenario.

So you would have to go with the cop out solution which is Person A suddenly decides he hates everyone because they small funny (or whatever) and does something about it.