When tragedy strikes and leaves seven-year-old Gaberiella an orphan, she must live with her grandparents Lord and Lady Fairfield in a gigantic, lonely mansion in England. Lord and Lady Fairfield expect Gabby to act like a lady, but she wants no part of it, so she retreats into a fantasy world of her own creation, amusing herself by making up stories and imagining secrets.

Thankfully, Patty, Gabby's maid, sees how sad and lonely the little girl is and decides to cheer her up by telling her about a strange door on the third floor of the mansion, shut tight and locked with a big padlock. Gabby immediately decides that her storybook world must be behind the door. She vows to do whatever she needs to do to get her little hands on the key to that lock-even if it means stealing it from Mrs. Middledorff, the housekeeper.

When her plan succeeds, and Gabby obtains the keys, she opens the door and steps into a room full of magical beings waiting for her arrival.