Pacifist surgeon Sir James Quentin (Sebastian Shaw) operates on Zaroff (Meinhart Maur), the inventor of a lethal weapon to be used against the Allies in the war. When Zaroff is discovered dead from an excess of ether, Quentin is immediately suspected. To clear her father's name, Quentin's daughter Pat (Patricia Roc) and her boyfriend Captain Mellish (Derrick De Marney) search for the murderer.