The crew of the U.S.S. Enterprise is exploring the seemingly peaceful and uninhabited world of M-3107 when a bizarre and inexplicable transporter accident causes both Captain Kirk and Dr. McCoy to vanish completely. Transporter records suggest that the two men were transported somewhere, but their ultimate destination remains a mystery.

Now in command of the Enterprise, Spock dispatches a search-and-rescue team - consisting of Security Chief Giotto, Transporter Technician John Kyle, and Chief Helmsman Hikaru Sulu - on an urgent mission to recover the missing officers.

But then the rescue team disappears as well!