When Max Monroe discovers an old detective agency in his grandfather's backyard, he also uncovers a spooky secret: the ghost of his great-uncle Larry! Max has always been obsessed with mystery books, so when Larry is given a second chance to prove he's a capable detective, they team up to help find a missing birthday girl. Can they rule out the many suspects—including a clown and a practical joker—before the birthday girl's mom comes home?