Underworld boss Frank Hoefle has evidence against him stolen, by his henchman Pinky, from the office of District Attorney Meredith, but is then stolen from Pinky, and the thief demands a ransom of $300,000 dollars for its return to Hoefle. The latter hires private detective Duncan MacLain and "Spud" Savage to follow the ransom-note demands and leave the money in a subway-station locker. Later, Eddie Miller, a pickpocket, lifts the locker key and MacLain follows him to an apartment house and overpowers Miller but not before he has sent the locker key up a dumb-waiter shaft. MacLain climbs up the shaft and finds Amy Arden with special prosecutor Paul Zarinka. He is knocked unconscious, and when he revives, Spud and Hoefle are there. Hoefle tells them to retrieve the evidence, "or else." Since he has a hard time telling the good guys from the bad guys, MacLain has a big job ahead of him. But he gets lucky and finds a 1914 newspaper story that explains all. (Most of the plot and much of the footage from this film was re-used in 1942 for Universal's "Gang Busters" serial.)