The Enterprise is sent to planet Ekos to investigate a disappearance of Federation historian John Gill. The Enterprise is attacked by an armed probe with a thermonuclear warhead, technology that is too advanced to be from Ekos or the nearby Zeon. When Kirk and Spock beam down, they find that Ekos has adopted a military regime similar to that of Nazi Germany, and is now at war with Zeon, and their führer is John Gill.

James Doohan (Lt. Cmdr. Montgomery Scott)
Richard Evans (Isak)
Valora Noland (Daras)
Skip Homeier (Melakon)
David Brian (John Gill)
Nichelle Nichols (Lt. Uhura)
Patrick Horgan (Eneg)
William Wintersole (Abrom)
Gilbert Green (S.S. Major)
Walter Koenig (Ensign Pavel Chekov)
Ralph Maurer (S.S. Lieutenant)
Ed McCready (S.S. Trooper)
Peter Canon (Gestapo Lieutenant)
Paul Baxley (First Trooper)
Chuck Courtney (Davod)
Bart La Rue (Newscaster)