Episode 4: The Survivors
Scenario 11: Old Friends (very last one)
Non spoiler quick explain: in last scenario where Jess is hanging off the bridge, save her.
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If you want the full ending with credits choose this action.
In one of the last scenarios of the last episode where you meet up with T-rex again, Jess is trapped hanging off a ledge. Two choices will present themselves. One button press on Jess and one on the can of dino DNA on the ground.
Choose Jess and you'll save her and earn this achievement.
Choose the can to have the Barbasolved achievement pop and say a sad farewell to Nima.
Choose wisely. ;>