Lieutenant Daniel Kwan kills himself by jumping into the plasma discharge in one of the warp nacelle tubes aboard the Enterprise, the only oddity being his comments about "they were laughing at me" and "I know what I have to do", before jumping. Captain Picard assigns Worf and Deanna Troi to investigate the death. Kwan's personnel logs and quarters reveal no traces of depression; in fact, he appeared to be happy to spend the next few days with his girlfriend, Ensign Calloway, and only had a slight but normal dislike for his superior Lieutenant Nara.
They talk to Nara at the nacelle but find that she had nothing against Kwan. Troi stands at the platform overlooking the plasma discharge and is suddenly awash with emotions, disorienting her. Dr. Crusher determines that her empathic senses were overloaded and suggests rest. Troi and Worf discuss that she may have been affected by an empathic "echo" left by Kwan, who also had weak empathic abilities. They return to the nacelle, where Troi experiences a series of visions: that of a woman backing away in fright from a red-haired man; equipment from Utopia Planitia, the starbase where the Enterprise was constructed; and later the same woman kissing another man in a closet. Worf breaks her out of these visions, and they determine that they were from events eight years ago during the Enterprise' construction. Troi is able to recognize the red-haired man as Lieutenant Walter Pierce, who is currently serving aboard the ship; Pierce had been Kwan's superior at Utopia Planitia as well. They speak to Pierce, but he claims to have no knowledge. After they leave him, Troi admits to Worf that she could not read Pierce, and believes him to also be partially empathic. As they prepare to retire for the night, Troi and Worf fall into a deep kiss, and spend the night together.
The next day, Dr. Crusher provides Troi with a neural inhibitor to block Troi's empathic sense to allow her to safely visit the nacelle. Worf is indifferent to Troi and instead provides her with Calloway to help. Troi, with Data and La Forge, examine the plasma conduit that Kwan was working before his death, and Troi is overcome with the same visions despite the inhibitor. She asserts there is something hidden in the conduit; La Forge discovers a human skeleton embedded in the ship, identified as Ensign Marla Finn, the woman from Troi's visions. Troi finds that Finn disappeared at Utopia Planitia before Kwan's arrival, and comes to suspect Pierce of killing her, believing the visions being from his point of view. She convinces Worf to arrest Pierce, but finds Worf taking more an interest in Calloway. Troi returns to her quarters and is surprised when Pierce arrives; fearing for her life, Troi tries to contact Worf but discovers he is in Calloway's quarters. She races there, and is shocked to find them hugging, and they turn to laugh at her. In a fit, she picks up a phaser and kills Worf. Shocked by her action, she stumbles out of Calloway's quarters, to find Pierce there; he tells her "you know what to do". Troi agrees and races to the nacelle tube and prepares to jump into the plasma like Kwan did before she is stopped by a very-much alive Worf.
Troi is broken out of her vision, and learns that it has only been a few seconds since she first arrived at the nacelle. Reviewing records show that Pierce, Finn, and the other man from her vision were all killed at Utopia Planitia from a plasma discharge, likely as a result of Finn seeing another man after being romantically involved with Pierce. She suspects Pierce was empathic, as she and Kwan had experienced the psychic residue from his death that still remains in the plasma conduit. With the case solved, Worf asks Troi about being surprised to see him after stopping her from jumping.