When Dick Spanner P.I. learns that Harry the Human Cannonball has gone missing (after he was fired), it can only mean one thing - trouble! During his investigations the persistent Lieutenant O'Grady tries to throw him in jail, 'The Fatman' gives Spanner some advice, Sidney Sidestreet offers no help at all and the villainous goons who work for the mysterious Mendoza try to kill him.