A thief is lurking around Penny's school. Money and mobile phones are disappearing more and more frequently. Ida's phone also falls into the thief's hands when she leaves it in the locker room during gym class. The possible suspects are actually very few: Penny's brother, Tim, who sprained his ankle and limped back to the locker room, the sour Ivy from the next class, and the daughter of Hemodipsucht. Penny and her detectives are conducting investigations, but all the suspects seem to be innocent... And now?