Set amidst the backdrop of World War II in England, three orphaned siblings, Carrie, Charles, and Paul Rawlins, are sent to the coastal village of Pepperinge Eye for safety. There, they are placed under the care of Miss Eglantine Price, an apprentice witch struggling to use her witchcraft to aid in the war effort. The children soon discover her secret when they observe her flying on a broomstick and, in an attempt to silence them, Miss Price casts a spell on a bedknob that allows the children’s bed to travel anywhere when twisted. Together with a magical book, the bedknob becomes the kids' ticket to a series of fantastical adventures.

The group's goal is to locate the second half of the book that Miss Price's spells come from, as she believes it will contain the spell of "Substitutiary Locomotion," which gives life to inanimate objects—a powerful tool that can be used in defending the country against enemy invasions. To find the missing spell, they join forces with Emelius Browne, a charming but inept conman and purported headmaster of the correspondence witchcraft school Miss Price attended. With the enchanted bedknob affixed to an old bed, they embark on a thrilling and magical journey that leads them to an animated, underwater realm, and later, to a bustling London marketplace. Their adventures are fueled by a shared sense of purpose and the unlikely yet steadfast camaraderie that develops between the makeshift family.