Spock, Sulu, and Uhura are delivering a stasis box from the extinct Slaver race on the shuttlecraft Copernicus. When they detect another box and follow its signal, they soon discover that a Kzinti privateer has set a trap. Capturing the Enterprise crew, they discover their box holds a rare find, a shape-shifting Slaver weapon. Now Spock and the others must keep the Kzinti from returning to their government with the weapon.