The Enterprise-D comes across a Federation transport under attack by two ships. The ships leave after the Enterprise arrives. The transport was ferrying a well known Lumerian ambassador, Ramid Ves Alkar (Lucia), to negotiations in the Rekag/Cironi system, which is why the transport was attacked. Starfleet decides to have the Enterprise transport Alkar to the conference, feeling that sending him on another unarmed transport would be to invite another attack. Accompanying Alkar is an old, irritable woman named Sev Maylor, who Alkar explains is his mother.
During the voyage, Deanna Troi and Alkar quickly find they are becoming friends. However, Maylor is jealous and threatens Troi to stay away from Alkar. Not long after this, Maylor dies, but Alkar seems unmoved by the loss. The ambassador asks Troi to assist him in the funeral rituals. During the ceremony, Alkar touches a funeral stone to one that Troi is holding and she feels some sort of shock. Not long after the service concludes, Troi becomes very nervous and irritable.
Beverly Crusher's medical examination of Maylor shows that there were unusually high levels of neurotransmitter residue present at the time of death. Doctor Crusher asks Captain Picard if she may conduct an autopsy, but Alkar states this would be a violation of Lumerian custom. Without evidence that the ship or crew is in danger, Picard is unwilling to risk such an incident.
Troi goes to see Alkar and, in a manner quite out of character, attempts to seduce him. When Alkar turns her down, she angrily leaves and instead propositions an ensign she encounters in the turbolift. When Commander Riker stops by Troi's quarters, the ensign is there with her, and hurriedly leaves. Troi then accuses Riker about being jealous of her and the ensign.
The Enterprise arrives at Cironia, and Picard and Alkar set to work. They meet with other members of Alkar's delegation including a woman named Liva. The negotiations between the disputing sides are going well.
Troi's behavior becomes more abnormal as she accuses one of her patients - an Ensign Janeway - during a counseling session of being a whiner. Troi's appearance is also changing: she now looks twenty years older and has taken to wearing revealing clothes. She goes to confront Alkar in Ten Forward and accuses him of flirting with Liva. She proceeds to make a scene and Riker escorts her out of the bar, and back to her quarters. Once there, Troi attempts to seduce Riker, but changes her mind and scratches his face. Shocked and confused, Riker hastily leaves. The next morning, Alkar informs Troi that he's going down to Circonia to conduct negotiations. Deanna angrily accuses Alkar of going to a rendezvous with Liva.
As the ambassador and his party are about to leave, Troi bursts into the transporter room to demandingly ask Alkar if he'd take her with him. Captain Picard is shocked at Troi's aged appearance. Troi proceeds to attack Alkar in the transporter room with a knife. She fails to stop him, Picard steps in between Troi and Alkar, and is wounded by Troi in the process. Picard insists that Alkar beams down to complete the mission as Troi is taken to sickbay.
Doctor Crusher runs an analysis which demonstrates that Troi has extraordinarily high levels of neurotransmitter activity, and is apparently suffering from the same affliction that befell Maylor. In light of new information, Picard approves an autopsy of Maylor's body. The autopsy reveals that not only was Maylor not Alkar's mother, but that she was only in her thirties. Picard and Worf beam down to confront Alkar.
Cornered, Alkar confesses that he has a strange ability to channel his unpleasant and negative emotions into other people, which enables him to be the perfect diplomat. Unfortunately, the channeling results in the aging and death of the recipients within a few years, whom he refers to as "receptacles." Although he admits Deanna's atrophy is unusually rapid, Alkar believes the end justifies the means, but Picard threatens to take Alkar back and charge him. However, Alkar refuses, and Picard and Worf are forced by security to leave empty-handed.
Crusher works out a plan to save Deanna. She temporarily induces death in Troi with Picard's permission, which causes Alkar to break his empathic link. Alkar senses that 'death', and Picard has him return to the Enterprise and to sickbay to see Troi's end. After this he goes to conduct a new 'funeral ritual' alone with Liva in his quarters. Beverly revives Troi just as the ritual is concluding. As Doctor Crusher begins a process of neurotransmitter decontamination, Alkar suddenly collapses, then lunges for Liva, desperate to complete a channel with her.
Liva is transported to safety, and Alkar, who is unable to cope with the dramatic overload of his pent up emotional feedback, ages rapidly and dies in seconds. Troi returns to normal in both attitude and appearance.