In this suspenseful melodrama, a bullet-ridden corpse turns up in the water off the New Orleans docks. To the police, he's a John Doe...until a public health doctor (Richard Widmark) discovers he carries a virulent strain of bubonic plague. Hundreds of officers are mobilized to track down the killers and all who had contact with the dead man in a desperate race against the clock before the highly contagious disease spreads far beyond the port area and puts the entire country in peril.