Mr Sideney was a student wizard of Unseen University who needed to earn a lot of money quickly to pay off his debts to the troll gangster Chrysoprase during the events of Hogfather. Foolishly he decided to join Mr Teatime (who insisted that his last name should be pronounced "Tea-ah-tim-eh") in his scheme to inhume the Hogfather. His role in the scheme is to open the magically sealed locks at the top of the tower in the Tower of Teeth in the Tooth Fairy's dimension and break into the Tooth Fairy's room. Over the course of the escapade, he begins to have second thoughts about working with Mr. Teatime as Teatime starts to increasingly demonstrate his psychotic behavior and Sideney begins to wonder if Teatime will kill him even if he succeeds. When he breaks into the room, he flees while Teatime is distracted and then finds that he has returned to his infant school, is five years old again, and is at the mercy of the school bully. In the film he is killed by the Scissor-Man.

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