Watson confronts a traumatic event from his Army days that still weighs heavily on him after his friend's wife reaches out begging for help when her husband is seemingly having a psychotic break; Shinwell is asked for one last favor by Moriarty.

Watson and the team are faced with an impossible choice when two lives hang in the balance, but they only have one vial of antidote available; Shinwell races to help the team; Watson goes head-to-head with Moriarty.