A frozen planet breaking apart, whose research station crew died strangely, leaving behind the contagion that strips the Enterprise crew of inhibitions.
Psi 2000 is an ancient, frozen world on the verge of breaking up. The Enterprise arrives in The Naked Time to observe its collapse and to retrieve a team of scientists stationed there, only to find them dead in bizarre circumstances, one frozen at the controls after shutting off life support.
A crewman on the landing party, Joe Tormolen, carries an unknown water-based agent back to the ship, where it spreads by touch and releases each crew member's buried emotions. While the crew falls into chaos, the ship's orbit decays toward the planet, and Scott and Spock must perform an untested cold restart of the engines to escape.