The Enterprise finds a small, disabled ship drifting in space and discovers it contains a human corpse. More questions arise when the Suliban and Tholians each claim the craft. Both alien species attack the Enterprise and later each other to seize the derelict.

When a massive alien vessel engulfs Enterprise, non-corporeal beings invade/possess the bodies of Trip and other crew members and hijack their souls. These non-corporeal beings claim to be explorers. But these "wisps" may not plan on giving the bodies back.