Eye of the Beholder

Lt Daniel Kwan, a seemingly contented engineer, throws himself into a plasma stream in one of the Enterprise's warp nacelles. Troi and Worf find nothing in his life to explain it. At the scene, Troi senses an empathic trace and begins having vivid visions of events from eight years earlier, when the ship was being built at Utopia Planitia. She sees a woman, a jealous red-haired man named Walter Pierce, and another man. Troi and Worf grow close and spend the night together. When a skeleton is found hidden behind a bulkhead, Troi believes she has uncovered a murder, and suspects a crewman still aboard. Then her visions overtake her completely: she sees Worf with another woman, kills him in a jealous rage and heads for the nacelle herself. Worf pulls her back in time. Pierce, who was part Betazoid, had killed Finn and her lover years ago and died with them, and his emotions left a deadly psychic imprint.