Mr. Gandiss and his son, Jack, ask Mr. Parker to help them stop the theft of brass from their airplane factory. While Jack and Penny visit the factory, a piece of brass is found in the possession of Sally Barker, and she is fired. Sally maintains that she has no idea how the brass came to be in her locker, and Penny believes her. With Jack and Sally's help, Penny attempts to bring the real thieves to justice