The Enterprise visits Caldos IV which has been terraformed to look like Scotland. They are there to enable Dr. Beverly Crusher to attend the funeral of her beloved grandmother, Felisa Howard, whom she called Nana. Several crew members attend the burial during which a still-teary Crusher sees a man she does not know but who is obviously very interested in the burial.
Later Crusher enters her grandmother's house, accompanied by Counselor Deanna Troi. Crusher reminisces tearfully as she looks over old pictures and mementos of her growing up with her Scottish grandmother while Deanna offers support and lets her cry.
Beverly takes several things onto the Enterprise. She also takes some diaries with her and reads them. She finds out that despite being 100 years old, her grandmother was involved with a 34 year-old man named Ronin.
Back on the planet a groundskeeper of her grandmother's tells her that there is a ghost in her grandmother's house and that she should leave immediately. He also tells her that she never should kindle a candle which her grandmother always carried with her. The candle would wake up the ghost.
He tries to take the candle with him, which angers Beverly slightly. She grabs the candle back and firmly orders him to leave and respect her privacy, since she needs time to grieve, not fret over the ghosts and superstitions over candles.
There she hears a voice who calls her name but she does not see anybody. The voice tells her that he is a ghost and loved her grandmother and now also loves Beverly. Finally he becomes visible and Beverly sees a man of about 30 years who tells her that he is not able to be visible for a long time.
Meanwhile, the colony is suffering from a major storm system, which the weather modification satellite is unable to correct. Data and Geordi attempt to fix the problem but are shocked to find Ned, the Howard groundskeeper, try to stop them, before he is killed in an explosion.
The ghost called Ronin manipulates Beverly's mind so that she falls in love with him. Ronin tells her to kindle the candle which Beverly has on the Enterprise. Beverly beams up, kindles the candle and Ronin appears. Beverly tells him that she has seldom loved a man as much as him in her former life.
Then Beverly tells Captain Picard that she wants to leave the Enterprise and to live on the planet from now on. Reluctantly, Picard agrees. Picard goes to Counselor Deanna Troi with whom Crusher spoke about Ronin before she left.
Troi tells Picard that Ronin is a very strange man but also that they have to accept Beverly's decision. Both are very worried about Beverly, especially since they notice how disheveled she has appeared lately and have seen dark circles under her eyes. They also know that rash, impulsive behavior is not in character for the reserved, cautious, and normally level-headed Beverly Crusher.
Then Picard beams down onto the planet and visits Beverly in her house. Beverly is lying flaccidly in a reclining chair, her usually neat hair unkempt and her dark blue eyes shadowed and appearing a strange shade of green.
He wants to get to know Ronin and finally Ronin appears. Picard asks many questions which Ronin does not want to answer and finally Ronin attacks Picard who falls down on the floor. Crusher wants to help Picard but Ronin wants to depart with her. Crusher insists on treating Picard and she does. Tears of relief fill her eyes when Picard comes to and reassures her that he's all right.
At the end Ronin goes alone to the cemetery where Geordi and Data have found an energy source in Beverly's grandmother's grave. Data and Geordi open the grave and the grandmother rises up and attacks them.
Crusher has already arrived and tells Ronin to get out of her grandmother's body. Ronin does, appears and tells Beverly to give him the candle. She has by then discovered that he was an anaphasic alien who could only survive because the candle was his energy receptacle.
Beverly destroys the candle with a phaser, and subsequently vapourizes Ronin when he attempts to possess her body. Then she sinks to the ground, deeply shaken and weeping.
Picard, Geordi, and Data are treated and recovered. Crusher also needs a bit of treatment, but her treatment, as Picard mentions in his log, will be 'personal'. Troi is the one who provides this for Crusher as she recovers both from her grandmother's death and from her ordeal with Ronin.