While staying at a hotel in England with his grandmother, Helga, a young boy named Luke inadvertently spies on a convention of witches. The Grand High Witch reveals a plan to turn all children into mice via a magical formula. When they discover the eavesdropper, the witches test the formula on him. Now, with the help of Helga and hotel manager Mr Stringer, Luke the mouse must fight back against the witches.

Four interwoven stories that occur on Halloween: an everyday high school principal has a secret life as a serial killer; a college virgin might have just met the one guy for her; a group of teenagers pull a mean prank, and a bitter old recluse receives an uninvited guest.