Orla is kicked off the squad when a library book she took out 400 years ago is overdue. The Mobile Unit must use budgeting to turn their $1 into $10 to pay the late fee, or else Orla will not get her badge back. There's a villain turning train cars odd, and the Mobile Unit must figure out the pattern in which the villain is striking. Oswald takes it upon himself to solve the train mystery just like his favorite book character: Detective Shmumbers.