The Transporter Malfunction (Mirror, Mirror)

Captain Kirk, Dr. McCoy, Scotty, and Uhura transported back to the USS Enterprise after initiating diplomatic relations with the peaceful Halkan Council. Interference from an ion storm, however, causes a transporter malfunction which sends Kirk, McCoy, Scotty, and Uhura to the ISS Enterprise in a mirror universe where the Federation is an evil Empire. In return, the mirror universe Captain Kirk, Dr. McCoy, Scotty, and Uhura are transported to the USS Enterprise, where they are locked up in the brig by Mr. Spock.