Kirk, Uhura and Chekov are set to beam down to examine and maintain a communications relay station, when they vanish from the transporter room in a way inconsistent with normal transport! They have been whisked across planetary systems by the mysterious Providers, who gather "inferior" beings from all over the galaxy and pit them against each other in blood contests. This activity is the only thing that stimulates the Providers. As the three begin their involuntary training, Enterprise begins following the scant evidence their abductors left behind, trying to locate them.

Spock senses the crew of Intrepid, a starship crewed solely by Vulcans, die. Enterprise investigates, and discovers a zone of darkness which conceals the hazard: an immense yet single-celled organism which drains energy from anything it encounters, as it did the Intrepid and her crew. And unless they can discover how to destroy it, Enterprise will be next. Worse, there are signs the organism has accumulated sufficient energy to reproduce...