Petty crook Harry Milgrim and his cousin, scientist Roger Braintree, plan to use a subsonic device developed by Braintree, which places people in an induced slumber, to rob Central City. Milgrim fakes his death to infiltrate the police station and steal valuable information, pinning the blame on Barry, who races against time to both prove his innocence and prevent Milgrim and Braintree from conducting a citywide robbery. In the end, he triumphs, with Milgrim and Braintree being arrested, clearing his name.