While staying at a hotel in England with his grandmother, Helga (Mai Zetterling), young Luke (Jasen Fisher) inadvertently spies on a convention of witches. The Grand High Witch (Anjelica Huston) reveals a plan to turn all children into mice through a magical formula. When they find that Luke has overheard, the witches test the formula on him. Now, with the help of Helga and the hotel manager, Mr. Stringer (Rowan Atkinson), Luke the mouse must fight back against the witches.