During a mission on a strange planet, Riker is wounded and stranded in a hospital without his communicator. While he is unconscious, his Malcorian doctors discover evidence that proves he is not of their race. When he comes to, Riker refers to himself by a Malcorian name and passes off his physical differences as deformities. His doctors, however, believe he is an alien, and decide to keep his presence a secret to avoid a panic among their people. Meanwhile, Picard and Troi surprise Mirasta, the Malcorian Minister of Science, when they materialize in her office.

Picard and Troi explain who they are and, to prove it, beam the enthusiastic Mirasta aboard the U.S.S. Enterprise. They explain that they have been monitoring her race for several years, and even have people stationed on her planet. When they tell her that Riker has been lost, Mirasta asks them to keep this a secret from her leader Durken, explaining that her society is in a transitory stage and many citizens are not ready to learn that they share the universe with other life forms. Back in the medical facility, Nilrem, one of Riker's doctors, begins spreading rumors that Riker's presence indicates a possible alien invasion.

Durken is beamed aboard the U.S.S. Enterprise, and while he is initially suspicious of Picard's motives, a conversation with Picard and a tour of the starship convinces him that the captain's intentions are not hostile. Meanwhile, Riker enlists the aid of an amorous Malcorian nurse to attempt an escape, but fails when he is cornered by a frightened mob of Malcorian citizens.

Riker's injuries are aggravated by the attack, and his doctors try once again to help him. Later, Durken returns to his planet to inform Security Minister Krola about his meeting with Picard, but Krola counters with a report that the Enterprise is attempting to infiltrate Malcorian society, and that one of their spies, Riker, has been captured. Mirasta leaps to Riker's defense, but Krola is dispatched to interrogate the alien and insists on reviving Riker with drugs that could harm him. Meanwhile, Picard goes to Durken to take responsibility for his actions and explain the reasoning for the secret surveillance. Durken understands Picard's position, but refuses to release Riker without further consideration.

After interrogating Riker proves useless, Krola shoots himself with Riker's phaser, placing it in Riker's hand to make it look like Riker did it. Soon afterward, Dr. Crusher materializes and takes both Riker and Krola aboard the U.S.S. Enterprise for treatment. She soon deduces that Riker was too weak to attack, therefore Krola did the actual shooting, pointing out that Krola will be fine since the phaser was set on stun. With his people's hysteria fresh in his mind, Durken asks Picard to cease the Federation mission on his planet until the Malcorians can be educated to accept this new view of the universe.