Summertime baseball doings on the Eastern seaboard and a mistaken theft are the stuff of a good mystery that keeps up suspense and good character portrayals to the end. Lefty, Pep and the rest of the Young Yankees want to beat their rivals the Young Dodgers so as to play a championship game with a team from another town- but they are dispirited when the money saved for uniforms disappears from their dugout. Detective work uncovers a prowler as a possible suspect, but the real culprit turns out to be Cocky, a boy who had pitched for the Dodgers last summer and been kicked out because he was a braggart. Jealousy made him want him want to tamper with the Yankees' records for his own former team, but unknowingly he took the money box instead. Full confession clears him honorably.