Skin of Evil

A shuttle carrying Counselor Troi home from a conference crashes on Vagra II. When an away team arrives, a pool of black ooze rises into a creature called Armus, which blocks the way to the wreck. As Yar tries to walk past it, Armus strikes her down with a burst of energy, and despite Dr Crusher's efforts she cannot be saved. Troi learns that Armus is the evil an ancient race cast off from themselves, left behind and consumed by spite. It torments the crew, even dragging Riker into its slick. Noticing that its force field weakens when its anger flares, Picard beams down and deliberately goads it, until the field fails and he, Troi and the shuttle pilot are beamed to safety. The Enterprise destroys the shuttle so that Armus cannot use it to escape, and the crew gathers for a holographic farewell that Yar recorded.