The Enterprise has taken on a delegation from a species called the Cairn, which is just learning a spoken language after communicating only via image-oriented telepathy. Lwaxana is on board to help train the Cairn to master verbal communication, and although her presence is as irritating as ever at first, it also becomes clear that she is feeling a fair amount of pain about something.

Maques, one of the Cairn, speaks to Deanna alone, concerned about what he calls a "dark place" in Lwaxana's mind. Deanna, however, interprets his comments as pertaining merely to issues of privacy, and reassures him that all is well. However, it soon is revealed that all is not well, beginning when Lwaxana comes to Ten-Forward and verbally lashes Riker for his friendship with Deanna. A medical exam reveals strong telepathic fatigue, but little else, and Lwaxana is ordered to get some rest. She disobeys this order, however, and as Deanna is showing the Cairn around the arboretum, Lwaxana suddenly collapses into a coma!

There is no apparent physical cause for her condition; it seems that her brain has simply shut down. Picard, concerned that it could be a side-effect of Cairn telepathy, asks Maques about it. Maques says that Picard's fear is unjustified, but adds that it is Lwaxana's "bad thoughts" that are causing her pain. When no one understands what he means, he attempts to explain telepathically to Deanna. The implications Deanna understands are that Lwaxana may have suffered some psychic trauma in the past that has caused her psyche to completely collapse on itself. Maques attempts to contact Lwaxana telepathically, but is unable to decipher the images he sees. He suggests a three-way link: Lwaxana, Maques - and Deanna.

Despite the risk, Deanna agrees to it. The link is established, and Deanna finds herself in a dark corridor on the Enterprise. She hears many things, including a cry for help from her mother, a splash of water, and a growling wolf; however, when she tries to locate the source of these sounds, barriers spring up around her. An image of Picard tries to order her away; a wolf chases her down the corridor; and an image of her father tries to distract her and keep her from continuing the search. Bypassing all of these obstacles, she suddenly sees an image of Hedril, Maques's young daughter - but before she can make sense of it, an image of Lwaxana herself appears, screaming at Deanna to "get away from here!" Deanna wakes, heart pounding.

Deanna speaks briefly to Hedril, who believes that her presence somehow saddens Lwaxana, but can give no other hints as to her presence in Lwaxana's mind. Deanna gets a copy of her mother's journal from Betazed, and as Lwaxana's condition worsens, Deanna and Picard find a seven-year gap in the journals, from a year after Lwaxana's wedding to just after Deanna's birth. Deanna decides that the only way to find the answers and to help her mother is to re-enter Lwaxana's mind. A second link is established...

... and she finds Hedril standing with the wolf. Hedril, however, does not answer to that name, and wanders off silently. Deanna pursues them, seemingly "off the edge" of the Enterprise into empty space, but finds herself in a mixture of an old home on Betazed and the arboretum. There she finds Lwaxana, alone and pitiful. Lwaxana tells Deanna to leave, but Deanna refuses, telling Lwaxana to let them face the truth together. Deanna sees a scene play itself out: a scene of herself as an infant, with her mother, her father, and an older sister, Kestra, whom Deanna never knew. Lwaxana finally tells Deanna of the tragic accident in which Kestra died, and with Deanna's help comes to terms with her own role in it. Lwaxana "says" goodbye to Kestra, and she and Deanna both wake, fully recovered. With Lwaxana returned to health, she and Deanna begin to talk about Kestra.