It's Halloween, and Horrid Henry can't wait to go trick-or-treating to get his hands on sweets. That is, until he finds out he must go trick-or-treating with Perfect Peter, who's wearing a bunny costume. Henry gives him a scary haircut, since he won't go with Peter dressed as a bunny, but he gets banned from going trick-or-treating by his mother. But will that stop him from getting sweets...?