Clyde is a hyperactive kid, and his twin sister, Claudia, does her best to keep him out of trouble--but after a class field trip to the science museum, and a zapped banana, he suddenly finds that excitement transforms him into a real monkey, which may help him catch the thief who took the golden monkey.

"Clyde has a secret. Whenever he gets too excited, he changes into a monkey. His twin sister, Claudia, is worried that this isn't good for him. But when a ghost is seen in their school's hallway, Clyde will have to use his monkey powers to save they day. Will Clyde ever be a normal boy again?--Jacket.