"Catspaw" by Robert Bloch
Star Trek's Halloween episode (aired 10/27/67). Written by the writer of "Psycho" and "Yours Truly, Jack the Ripper." He also wrote the episode "What are Little Girls Made Of?"
Sulu, Scotty, and Jackson are missing on a planet with no signs of life. Jackson calls for beam up, but he's dead when he gets aboard. Kirk, Spock, and McCoy beam down to the planet to investigate. Fog appears with no weather-related reason and 3 witches from the Scottish play warn them off. (One of my fave lines: SPOCK: Very bad poetry, Captain.)
They read life signs and follow them to a creepy castle with a gorgeous black cat. Then they fall in a pit trap and wake chained to the wall. Scotty and Sulu, mind-controlled, come to fetch them and they try to overcome them but are suddenly in another room. There they meet Korob, who looks like a wizard. Korob seems to consult with the black cat like a familiar. Korob admits they are not native to this world. He invites them to eat, then tries to bribe them with gems. (They have no value because "We could manufacture a ton of these on our ship.")
The cat leaves and in walks Sylvia, wearing a diamond pendant just like the cat. She states that she killed Jackson with sympathetic magic, and demonstrates with a model Enterprise over a flame. Allowing Kirk to contact the ship, he finds they're burning up. Kirk surrenders and Korob puts the Enterprise model into crystal, which acts as a force field, keeping anyone from beaming down. (KOROB: Captain, you've seen something of our science. Now tell us about yours.) KIrk and Spock are taken back to the dungeon while Sylvia interrogates McCoy. Kirk and Spock speculate they pulled their scenarios from the unconscious. McCoy comes back zombified.
Korob and Sylvia argue. Sylvia is enjoying the new sensations their humanoid forms give them. Kirk is brought to her and Korob leaves. She admits they come from a world without sensation, so Kirk tries to seduce her. She realizes he's playing her and gets pissed off. Meanwhile on the ship, they manage to put a dent in the force field.
Korob frees Kirk and Spock and has freed Enterprise. But Sylvia has transformed herself into a very large cat and is stalking them. They end up back in the dungeon and Sylvia pushes the door open onto Korob, killing him. Kirk grabs his wand and he and Spock go back up through the hole they fell through. They end up having to fight off Sulu, Scotty, and McCoy, knocking them out.
Sylvia appears, grabs Kirk and transports them back to the dining hall. She tries to win him over then threatens him with a phaser. Kirk smashes the wand, breaking their transmuter. There is a flash of blinding light and the crew - back to themselves - find themselves outside. Nearby are Korob and Sylvia as they really are, and they die.
For some reason, I thought I recalled this as a bad episode and it isn't. It's not top tier, but it's a perfectly acceptable adventure. Shatner does a nice job messing with Sylvia and Theo Marcuse does his usual fine job as Korob. Antoinette Bower does well at showing how Sylvia is enjoying her new sensations. The aliens' true forms are creepy looking puppets that are actually kind of pathetic. I felt a little sorry for them. I love Sylvia's outfit btw. Maybe I'll cosplay her someday.
"CATSPAW" always has a special place for me because Halloween is my favorite holiday, and it really IS a solid episode.