A water-borne agent picked up at the disintegrating planet Psi 2000 spread through the Enterprise crew, stripping away inhibitions while the ship was falling toward the planet.
While observing the breakup of the frozen planet Psi 2000, the Enterprise beamed back a landing party from a research station where the scientists had died in bizarre circumstances. Crewman Joe Tormolen carried back a contagion that behaved like alcohol, releasing hidden emotions, and it passed from person to person through perspiration. Sulu roamed the corridors with a sword, Kevin Riley seized engineering and shut down the engines, and even Spock lost his emotional control.
McCoy developed a cure, but the ship's orbit was decaying. Spock and Scott attempted an untested cold restart of the warp engines, which saved the Enterprise and threw it about three days back in time.