Orbiting aimlessly without a crew, the USS Exeter presents the appearance of a Marie Celeste in space to the incredulous eyes of Captain Kirk and his boarding party, but they soon find something far more sinister than was seen in that ancient mystery of the sea.
Confirming their fears, the captain's log warns - 'If you've come aboard, you're dead men - don't go back to your ship!' The only alternative is the planet below... and the Yangs are coming!