Stella, her bestie Roger, and her second-best friend Owen are excited to go see Sue the T-rex at the museum, but when Owen has to leave early because he lost a tooth, Stella becomes determined to find it for him. How did he manage to lose a tooth? Was it stolen? Could the tooth fairy be responsible? Could Owen be...a dinosaur boy?

Nothing will keep Stella from her investigation, even if she and Roger fear their own teeth could be stolen too. But the more Stella investigates, the more she realizes that perhaps this case is not as complicated as she thought.