"Catspaw" is an episode of the second season of the original science fiction television series Star Trek. It is episode #36, production #30, and was first broadcast October 27, 1967 and repeated on May 24, 1968. It was written by Robert Bloch, and directed by Joseph Pevney. Its gothic horror elements are perhaps best explained by the proximity of the episode's release to Halloween. Writer Robert Bloch based his teleplay very loosely on his short story "Broomstick Ride".
In this episode, two powerful aliens threaten the well-being of the Enterprise and her crew.
On stardate 3018.2, the Federationstarship USS Enterprise, under the command of Captain James T. Kirk, explores the apparently lifeless planet Pyris VII. Chief Engineer Scott, Lt. Hikaru Sulu, and crewmember Jackson are sent down to explore the surface. The ship soon loses contact with Scott and Sulu; Jackson is transported back to the ship, but falls from the platform dead. His lifeless body emits an eerie voice telling Captain Kirk that the Enterprise is cursed and must leave the planet immediately, or everyone will die.
Kirk beams down with First Officer Spock and Chief Medical Officer Dr. McCoy to search for the missing crewmen. The landing party comes upon three apparitions that appear as witches, who warn the landing team not to proceed any further. The team ignores the warnings and discovers what appears to be a medieval castle.
Upon entering the castle, the landing party comes across a black cat that wears a sparkling diamond pendant. As they follow the cat, the floor collapses, and the fall knocks them out. When they come to, they find themselves held in irons in a dungeon. Scott and Sulu soon appear as mindless zombies, controlled by an unknown force. Kirk and the others attempt to overcome them but find themselves teleported to another part of the castle, where they encounter a robed man, Korob, and the black cat, whom he appears to consult for advice. Spock questions Korob about why previous surveys of Pyris VII indicated no life on the planet. Korob replies that he is not a native of the planet.
The cat leaves the room, and Korob's beautiful colleague Sylvia soon appears. She wears a diamond pendant, identical to the cat's, around her neck. When Kirk demands that Scott and Sulu be released. Sylvia dangles a miniature model of the Enterprise over a lit candle, and the crew of the real Enterprise reports a rapid rise in hull temperature. Kirk reluctantly surrenders and offers to cooperate.
Korob places the "voodoo model" of the ship in a crystal cube, where the sensors aboard the real Enterprise show the ship to be encased in an impenetrable force field. Kirk and Spock are led back to the dungeon, and McCoy is zombified like Scotty and Sulu. Sylvia takes an interest in Kirk and changes into different attractive forms to test his emotions. Sylvia tells Kirk that she and Korob are explorers from another galaxy. They wield their power through a device called a transmuter, which gives them control over matter. Sylvia decides Kirk is using her and becomes angry, sending him back to the dungeon.
Korob comes to free Kirk and Spock, tells them that he has released their ship, and urges them to leave immediately, as he can no longer keep Sylvia under control. Sylvia discovers Korob's realignment, changes herself into a giant cat, and attacks him. Korob releases his scepter and Kirk picks it up, guessing it to be the transmuter. Kirk tells Sylvia that he has the transmuter, and he destroys it when Sylvia threatens him with a phaser. The castle disappears, and Sulu, Scotty, and McCoy return to normal. Looking down at a nearby rock, Kirk spots two tiny creatures that resemble blue and yellow stick bugs: they are Korob's and Sylvia's true form. Unable to survive without their transmuter, the two creatures die and disintegrate.