It's Samantha and Darrin's first wedding anniversary, and Aunt Clara stops by unexpectedly to provide her best wishes and a gift for each. Darrin's gift, a golf cap, is too small, so Aunt Clara recites an incantation to resize it to fit his head. The incantation does match the cap size to the head, but instead of making the cap larger, it makes Darrin's head smaller by turning him into a small chimpanzee. Aunt Clara has no idea what she did wrong, and can't remember the incantation to undo the spell. As Aunt Clara tries to break the spell, Darrin has to avoid Larry Tate and work, and a nosy Gladys Kravitz. In trying to achieve both, Darrin gets into a bit of trouble, and in the process goes missing, Samantha, Endora and Aunt Clara not knowing that he has been captured by the local zoo-keeper. Samantha hopes they can find him and that Aunt Clara can break the spell, since Samantha has some important news for him.
