While en route to the Morgana Quadrant, the U.S.S. Enterprise is engulfed by a mysterious "hole" having no dimensions and void of all energy and matter.

Captain Picard is perplexed by this mysterious oddity which cannot be measured or defined in human terms, and the crew is caught in a trap which, by their standards, does not even exist.

Unable to escape from the powerful hole, Riker and Worf decide to investigate an abandoned starship also marooned in the trap. On board the ship, the officers are confounded by a series of inexplicable incidents, but return safely to the Enterprise.

The crew is then confronted by a giant human eye which peers in at them through the main view screen. The being, calling Itself Nagilum, explains that he is using the Enterprise in an experiment to study human life — specifically, the many ways in which humans die. Wishing to observe death in all of its forms, Nagilum plans to use one-third to one-half of the crew as human guinea pigs.

Unwilling to stand by and watch his crew being slaughtered, Picard makes one of the most difficult decisions of his career. With Riker's support, Picard initiates the auto-destruct system of the ship — within 20 minutes, the Enterprise and her crew will be destroyed.

But as the sands of time slip away, Troi, Data and Geordi plead with Picard to reverse his decision, pointing out the futility of killing everyone on board just to spite Nagilum. While Picard wonders whether Nagilum is bluffing, the Enterprise is suddenly freed from the black hole and the captain is able to revoke the auto-destruct command with only two seconds to spare. Nagilum tells Picard that he observed enough watching the crew prepare to die to help him understand human nature, and Picard points out that they share one characteristic: curiosity.