Investigating a sector of space where starships have disappeared every 27 years, the U.S.S. Enterprise male crew are attracted by a mysterious signal. Kirk beams down with a landing party and encounters a race of beautiful women who survive by drawing the energy from the male members of the ships that they have lured to their planet.

Patrolling near the Neutral Zone, the U.S.S. Enterprise finds a ship and rescues Carter Winston, a Federation citizen, financier, and philanthropist missing for 5 years. However, Winston turns out to really be a Vendorian, an alien species that can transform its shape at will. He is also allied with the Romulans.