The Aldens help out at a minor league stadium and investigate when it appears someone in the ballpark is stealing the home team pitcher's signals and relaying them to the batters of the other team.

Eighth-grader Molly's ability to throw a knuckleball earns her a spot on the baseball team, which not only helps her feel connected to her recently deceased father, who loved baseball, it helps in other aspects of her life, as well.