Catspaw

Episode: Season 2 Episode 7
Air Date: October 27th, 1967

When an away team member returns to the Enterprise alone, he dies as he re-materializes. His corpse speaks a warning, that the ship is cursed and must leave the planet immediately. Kirk's response is to beam down with Spock and McCoy to search for Sulu and Scotty. They are greeted by a projection of what appear to be three witches warning them to return.

A castle, black cat and dungeon later, they meet Korob who appears Korob has the ability to create illusions. Korob claims to have been testing humans in loyalty, bravery and integrity.

Of course the black cat leaves and a women, Sylvia, immediately shows up and talks about how they can control the minds of people. Kirk takes back his weapon and demands answers. Sylvia responds by putting a toy version of the Enterprise over a flame and the real Enterprise starts heating up too. Kirk surrenders his weapon to stop her from destroying the Enterprise.

Sylvia has a fight with Korob and Kirk uses it as an opening to seduce Sylvia to find out information of what give her power, a device. This convinces Korob that Sylvia must be stopped and he is killed helping Kirk and the away team escape. In the final showdown Kirk ends up with the device and destroys it which reverts all illusions and Korob and Sylvia die unable to survive on their own.

"He doesn't know about trick-or-treat" - McCoy