The Federation starship Enterprise, under the command of Captain Jean-Luc Picard, is assigned to transport Salia, the future ruler and dauphin of Daled IV, and her governess Anya from a planet where she voluntarily exiled herself. Her parents, rulers of two opposing factions on Daled IV, recently died, and Salia represents a chance to bring unification to the two factions. As such, Anya is overly protective of her. On board, Salia meets young Acting Ensign Wesley Crusher, who becomes smitten with her. Crusher receives courtship advice from the crew members, and the two form a bond. He introduces her to Thalian chocolate mousse in Ten Forward, and takes her to the holodeck to show her several other worlds after Salia expresses an interest in exploring the galaxy.
When Anya, touring the ship, discovers a crew member with a virulent disease being in a containment field in Sickbay, she demands the crew member be killed to protect Salia. Chief Medical Officer Dr. Pulaski refuses and insists the disease is contained, but Anya transforms into a large monstrous form, easily matching Lt. Worf's strength when he tries to intervene. When Captain Picard arrives, Anya reverts to her petite humanoid form and defiantly explains her actions. Dr. Pulaski identifies Anya as an allasomorph, a shapeshifter, who could present a danger for the crew. Picard orders Anya to be confined to quarters, and Worf, as head of security, promises to Anya to watch over Salia. Picard, aware of Crusher's attraction to Salia, asks him to stay away from Salia, to which he agrees. At night however, as Anya is sleeping, Salia slips out of their quarters and visits Crusher. Anya soon discovers Salia's disappearance, and bursts into his quarters, transforming into the same giant beast as before. To Crusher's surprise, Salia also transforms into a similar beast, holding Anya at bay. Both revert to their human forms as security arrives. Later, Salia attempts to apologize to Wesley for her deception, but Crusher refuses to listen.
The Enterprise arrives at Daled IV with no further incidents. As Salia prepares to depart, Anya reveals she will not be going with her, instead returning to her home on an orbiting moon. Anya also warns her that she will unlikely be able to leave the planet once she has taken the leadership role. Salia thanks Anya for her upbringing before Anya departs. Just before Salia is to be beamed down to the planet, Wesley Crusher arrives to say his goodbyes, bringing her one last taste of chocolate mousse. Salia thanks him, and then transforms into her natural form before she is beamed down to the planet.