A contagion strips away the crew's inhibitions while the Enterprise races to avoid a collapsing planet.
The Enterprise arrives at the disintegrating planet Psi 2000 to observe its breakup and collect a research team, but Spock and Lieutenant Joe Tormolen find the scientists frozen to death in bizarre circumstances. Tormolen removes a glove and touches a red liquid, and back aboard he grows erratic, turns a knife on himself and dies despite surgery. The condition passes by touch: Sulu roams the corridors with a fencing sword, Kevin Riley seizes engineering, shuts down the engines and declares himself captain, and Spock loses control of his feelings after Christine Chapel confesses her love for him.
As the ship is dragged toward the planet, McCoy identifies a water-borne molecular chain that acts like alcohol and produces a cure. Scotty attempts an untested cold-start of the warp engines, which flings the Enterprise free and back 71 hours in time. Written by John D. F. Black, the story was later revisited by The Next Generation in The Naked Now.