Ensign Peter Kirk asks his uncle James to marry him and his lover, Lt. Alex Freeman. But first both of them join a security team headed by Mr. Spock investigating a distress call by the U.S.S. Copernicus.

Spock, Peter Kirk & Alex Freeman are stuck aboard the U.S.S. Copernicus which is invested with Regulan Bloodworm and has to be destroyed. However, they meet two researchers aboard who claim to have a cure for the infestation.