After answering a distress call from a remote Federation planet under attack, the crew of the U.S.S. Enterprise is shocked to discover that all but two of the 11,000 inhabitants have been killed.
Beaming down to Rana IV, the Away Team finds that the entire planet has been obliterated, except for a patch of land where an undamaged home still stands. Inside, they meet the sole survivors of the attack — Kevin and Rishon Uxbridge, an elderly couple who cannot explain why they survived the devastation and refuse to leave the decimated colony.
Meanwhile, back on the Enterprise, Counselor Troi's head is inexplicably filled with music which continues to repeat unabated, day and night. She confesses her problem to Picard and admits that she is unable to read the emotions of the Uxbridges as a result.
Suddenly, the ship that attacked Rana IV returns to the area and fires upon the U.S.S. Enterprise, crippling the starship's weapons systems. In sick bay, Dr. Crusher tries to relieve the incessant music in Troi's brain by heavily sedating her, then inducing a coma, but nothing seems to work.
Following his hunch that the warship somehow responds to the Uxbridges' wishes, Picard confronts them. Though Kevin angrily insists that he and his wife do not require the crew's help, Picard tells the couple that the U.S.S. Enterprise will remain in orbit as long as the two of them are alive.
A short time later, the warship reappears and obliterates the Uxbridges' home. In response, the Enterprise destroys the warship. Despite the fact that the crew can find no signs of life on Rana IV, Picard insists upon keeping the planet under surveillance.
Within hours, Geordi reports that the Uxbridges' home has reappeared on the planet — what's more, the couple is alive and well inside it! Picard beams them up to the ship and forces Kevin to admit that his home, his wife and the warship are merely reproductions of the originals, which were destroyed in the attack.
Kevin confesses that he is a Douwd, an immortal being capable of creating disguises and false surroundings. He explains that after taking a human form 50 years ago, he visited earth and fell in love with Rishon, who remained unaware of his true identity and magic powers throughout their marriage.
Unfortunately, when the aggressive species known as the Husnock attacked Rana IV, Kevin refused to fight back or kill anyone. However, his wife joined the battle and was murdered by the Husnock, along with everyone else in the colony.
Enraged by his wife's death, Kevin then summoned his magical powers and in an instant of grief, destroyed the Husnock race of 50 billion. Fearful that Troi would discover his secret, Uxbridge put the music in her mind to block her telepathic powers.
Stunned by Uxbridge's confession, Picard tells Kevin that he is not qualified to judge his crimes and returns the man to his planet. But before leaving the Enterprise, Kevin restores Troi to normal.