Steve takes his class to the circus where they observe a human fly fall from his prop. He is not seriously hurt but he doesn't want to go back out as he has lost his nerve. When crimes at great heights begin to occur, Cap suspects the human fly, but when he confronts the circus performer he claims one of his costumes has been stolen by another. Cap sees a newspaper article about a valuable stamp collection kept in a lighthouse and figures the human fly will make a go for it. Cap and Bucky have guessed right, and when the fly kicks over a jar of molasses while attempting to flee from them, he is caught and revealed as a window washer.