Star Trek: The Next Generation - Season 4 Episode 17 -

The Enterprise has finally tracked the missing starship USS Brattain. Counselor Deanna Troi senses trouble with the life on board and joins Riker's boarding party. The crew was slashed to death; the only survivor, Betazoid Counselor Andrus Hagan, is in shock. Doctor Beverly Crusher 's autopsy concludes 34 crewmen killed each other with phasers and other weapons, even bare hands; a tape recorded a paranoiac fear among them. While the Enterprise tows the Brattain to the nearest starbase, its own crewmen starts sensing another presence and experiencing rising fear, ...