An archaeological dig releases a parasitic extradimensional threat that sparks a hostage crisis aboard the Enterprise.
Security officer Dennis Gamble and Beto Ortegas join Chapel and Korby on an expedition to an ancient structure that may hold the secret of immortality. Gamble picks up a glowing orb that explodes and destroys his eyes, and the away team discovers that the building is a prison for the Vezda, parasitic extradimensional beings, before escaping.
Back aboard the Enterprise, Batel attacks Gamble, sensing that he is possessed. Gamble breaks out of custody and takes hostages, and Pelia kills him to end the crisis, while Scotty traps the Vezda spirit in the transporter pattern buffer. The horror-tinged episode introduces the Vezda and Batel's ability to sense them, threads that return in the season finale, New Life and New Civilizations, where the prison and its guardian become central. Andi Armaganian directed from a script by Onitra Johnson and Davy Perez.