Antonio Riccardi, a rare stamp dealer who is secretly a hired killer, pays for the violin lessons of his gifted brother Giuseppe. To meet the expenses of Giuseppe's concert debut he accepts a further job, but his decision to do so provides Detective Inspector Carson, who has long hoped to ensnare Tony, with an opportunity that might now enable him to bring about his downfall.

British diamond smugglers use the radiowoman (Phyllis Kirk) from a freighter docked on the Thames to unwittingly "mule" their swag, hidden in cigarettes, past customs, not knowing that she has befriended an Inspector for the Thames River Patrol.

Picking a pocket leads to blackmail and murder for a petty criminal in London.