Kit is the son of the Queen's witch doctor and takes his best friend, Prince Henry, on a night time ride on his magic carpet to see the werewolves in the Tower of London. But when Henry falls into the den and is bitten, Kit is forbidden to see him and the Queen sends for Stafford Sparks, the Royal Superintendent of Scientific Progress, to cure Henry with electricity. Kit decides he must rescue his friend and prove to the Queen that magic is still alive - but his attempts end up leading him into the tunnels under London, and into terrible danger.