Johnny Evans, British secret agent, was appalled and frightened at the way things were going. It was inconceivable that an American submarine captain could deliberately torpedo an American destroyer. It couldn't happen—but it did.

Yet this, he knew, was only the latest incredible episode in a disastrous wave of treachery that was spreading everywhere. In Britain, in the Pacific, in Russia, some of our most trusted men were selling out to the enemy. Was moral disintegration on a wholesale scale setting in among the Allies? Or were these men the victims of on ingenious secret weapon with the power to make them traitors against their wills?

From the wreckage of the American submarine comes a vital clue, taking Evans from Portsmouth, England, to an obscure American college on the Hudson and a mysteriously absent professor of psychology—to a desolate Long Island beach for a midnight rendezvous with on enemy submarine to Yorktown to investigate the very suspicious activities of a man named Kleiner.

But it is not until Maddy Sawyer, slim, lovely British agent, is marked as the next victim that the whole diabolic picture swings into focus, and the FBI closes in.