Beyond the Knock-Knock Door — Scott Monk

Michael, Luke, and Samantha Bowman prove that trouble always comes in threes. The 12-year-old triplets have accidentally crashed a school bus, been banned from supermarkets for playing ice hockey with frozen chickens, and attracted the ire of the school bullies. When they are invited to a costume party, they cross paths with Mr. Goode Deed -- owner of a run-down costume shop filled with strange artifacts. With his help, they attend the party dressed as a knight, pirate, and star ranger. However, rather than enjoying cake and sausage rolls at the party, the triplets find themselves at the center of more trouble. The bullies chase them into the city sewers, where they become trapped. During their search for an exit, they discover a Knock Knock Door. It's a mischievous portal to any planet in the universe that is opened by answering a riddle.