Star Trek VI: The Undiscovered Country
When Kirk and Bones are sentenced to live out the rest of their lives in the Klingon prison Rura Penthe, escape seems impossible. But then a hot shapeshifter named Martia shows them a secret pathway out of the jail. Kirk, of course, makes out with her. She, of course, turns into another Kirk and tries to kill them both. Luckily, Spock swoops in and beams his pals to safety.