Zoe Elwood's know-it-all brother Kelby has started the Northern Spy Club-named after a variety of apple in their father's Vermont orchard-and declared himself President. To get into the club one must walk a narrow beam over rusted farm machinery, and solve a crime. In this case, the crime involves Alice Fairweather's grandmother, who has expired after eating a bowl of pea soup. According to Kelby, the elderly Bagley Sisters across the street who made the soup must be guilty. But Zoe is fond of the Bagley Sisters and asks her friend Spencer to help her uncover clues that will prove the sisters are innocent. Solving the crime and walking the high beam in the barn are something that Zoe is determined to prove a girl can do just as well as a boy.