In 'Operation P.I.A.N.O.', a hamster is sent to replace Number Four for disobeying orders and smashing a piano; in 'Operation Z.O.O.', the Kids Next Door are captured by a children's zoo to be their kid exhibit.
The Kids Next Door try to quietly defend their treehouse from attack while Number One takes a nap; Number Three accidentally takes a mysterious stranger with her to visit Rainbow Monkey Island.