Hurray! Tracy will be the queen of the carnival! This will be remembered for a long time. But a series of daring robberies darkens the anticipation of the holiday for the residents of the town. Holly and Belinda suspect that Tracy's new friend Mark and his parents were involved. After all, for some reason they are robbing the very houses where Mark’s mother had visited the day before. And his dad performed magic tricks in these houses - always with the master’s keys. And their son is such a piece of cake: lying, cheating is a piece of cake for him. Members of the Detective Club simply cannot ignore such an exciting mystery...