For his birthday, Calvin's mother gives him two tickets to see Lomax the Magnificent (magician and hypnotist extraordinaire!). Even though Mama hints that his little sister, Trudy, would love to go, Calvin doesn't hesitate to invite his friend Rodney instead.

The boys return home greatly impressed by the magician's performance. When Calvin's mother goes out, she leaves him in charge of Trudy. It's a job Calvin dislikes because his sister does not want to be left out of anything. So Calvin and Rodney include her--by making her the first subject for their own hypnotizing machine.

Much to the boys' surprise, the machine works. But unfortunately they cannot undo what they have done. Trudy is stuck in her trance, convinced she is a dog--panting, drooling, and barking at squirrels. The only problem is, Calvin can't remember Lomax's magic word--Probuditi!--so Trudy won't snap out of it!

The boys are worried and decide to take Trudy to the one man they know can solve their problem--but will Lomax help them? Mama is on her way home . . . Who will have the last laugh?