Dr. McCoy receives an accidental overdose of a powerful medication and becomes dangerously paranoid. He escapes into Earth's past and there changes history in a way that prevents the Federation from ever having existed! Kirk and Spock must follow their deranged friend into the past to rescue him and set right whatever McCoy changed, or they will be stranded in the past forever.
9/10 (4 Votes cast)
Warning: Star Trek season 1 episode 28 guide may contain spoilers