Catspaw

Kirk beams down with Spock and McCoy, leaving Assistant Chief Engineer DeSalle in command of the ship. They arrive in a fogbound environment, quite at odds with what their sensor readings indicated. Detecting lifeforms nearby the landing party investigates, only to be confronted with a ghostly apparition - three witches, warning them to leave or face disaster. Undaunted, the officers press on and discover a large castle. They enter and begin to explore, but a section of floor collapses beneath them, knocking them out.

They wake to find themselves chained in a dungeon. Scotty and Sulu appear, but they appear to by drugged or hypnotised, not recognising their fellow officers. They free the landing party and take them at gunpoint from the room to meet a robed man. He is, apparently, some kind of magician - complete with a wand and black cat. The man's name is Korob, and he appears intent on getting the Enterprise officers to leave as soon as possible. Korob claims that the events have been staged to test the Enterprise crew, but he clearly seems to be hiding the truth.

A woman, Sylvia, enters. She demonstrates her own power to Kirk, holding a small model of the Enterprise over a candle - and action which causes the real ship in orbit to grow unbearably hot! Although she spares the ship, Korob seals the model in a glass block, which paralyses the real ship within a strange forcefield.

Kirk and Spock are taken to the dungeon, whilst Sylvia questions McCoy. She argues with Korob about their plans - Sylvia states that she enjoys the sensations she is experiencing in her present form, as apparently their normal existence does not afford them such. Korob argues that they have a mission to complete, but Sylvia seems in favour of abandoning it.

Sylvia brings Kirk back to talk, and reveals that she has become enamoured of him. She is thinking of getting rid of Korob and keeping Kirk for herself. Kirk plays along for information, and learns that the "magic wand" is a transmuter, able to reform matter into different forms - this is how the pair create the various strange things Kirk has encountered. She realises the deception and has Kirk returned to the dungeon.

Korob, beginning to fear Sylvia's intentions, releases the Enterprise and Kirk and Spock. He expresses regret for how things have gone, wishing there could have been peaceful contact. As they attempt to flee, Kirk and Spock encounter Sylvia's black cat, only grown to enormous size. The cat kills Korob, and Kirk grabs his transmuter wand and escapes. Sylvia demands the transmuter wand, which is more powerful than her own device, but as Kirk begins to hand it over he instead smashes it. At once the castle and everything within it vanishes, leaving only Sylvia and Korob in their true form - two small, vaguely birdlike aliens who quickly die. With the menace defeated, the officers beam back to the ship.

Overall, just not a good episode.