The crew is stunned by the suicide of Lieutenant Kwan, who jumps into the plasma stream by his work station in Nacelle Control. Troi and Worf investigate, and they are baffled as to why the seemingly well-adjusted crew member would take his own life. The woman he was dating, Ensign Calloway, is equally shocked, as is Lieutenant Nara, Kwan's supervisor, who remarks that Kwan seemed normal the day he took his life. Troi climbs the ladder toward the catwalk from where Kwan jumped, and is suddenly overwhelmed by a sense of panic and fear.
Since Kwan was a partial empath, Beverly wonders if Troi picked up an empathic echo he left behind before his suicide. She urges Troi to be careful when returning to Kwan's station, and Worf consents to accompany her. As the two work together, hidden feelings hint at surfacing, but both resist. Later, they return to Nacelle Control and Troi climbs the ladder, abruptly finding herself in an unfinished version of the same room. She encounters a terrified woman and comes face-to-face with a strange, staring man before realizing Worf is nowhere to be seen.
Still disoriented, Troi sees the woman again, now embracing another man, and joining him in laughing at Troi. She then finds Worf and returns to reality. When Picard hears the room's description, he suggests that Troi saw something from the time of the ship's construction eight years before — a project in which Lieutenant Kwan participated. Troi feels she may have been seeing something through his eyes, and she and Worf research personnel files from the construction project. Troi recognizes the staring man as Lieutenant Walter Pierce, who currently works in Engineering. She and Worf question Pierce, but he claims not to remember working with Lieutenant Kwan back then. Troi senses Pierce has empathic ability, and that he is hiding something. Later, Worf walks Troi back to her quarters, and they give in to their building feelings and kiss passionately.
After spending the night together, Troi and Worf continue their duties. Beverly administers an empathic inhibitor to Troi, and she returns to Nacelle Control, while Worf stays in Sickbay to work with Calloway. Geordi opens the panel on which Kwan was working the day he died, and Troi suddenly sees the faces of Pierce and the terrified woman. Data and Geordi scan the wall behind the panel, and they find portions of a human skeleton, identified as the remains of the woman Troi saw. Since Lieutenant Kwan didn't start work on the U.S.S. Enterprise until six months after the woman's death, Troi realizes she didn't see the event through Kwan's eyes — she saw it through Pierce's. Worf goes to meet Pierce, while Troi returns to her quarters, and is shocked when Pierce arrives at her door.
Pierce tells Troi that Worf went to Calloway's quarters, and Troi rushes over to find Worf and Calloway embracing, then laughing at her. Overcome with jealousy, Troi grabs Worf's phaser and kills him, then runs to Nacelle Control and prepares to jump into the plasma stream. Suddenly, a hand pulls her back, and she turns to see Worf, alive. Troi notices everything is the same as it was when she and Worf first came to the nacelle tube together, and realizes the entire experience since then occurred in her mind. Later, she learns that Pierce and the laughing couple had died in a plasma discharge eight years before. Troi surmises that Pierce caught the other two having an affair, killed them both, activated the plasma stream to obliterate the evidence, then committed suicide. Because Pierce was part empath, both Kwan and Troi picked up the empathic signature he left behind. Fortunately, in Troi's case, tragedy was averted.