A strange, red circle appears on the neck of a man saved from the guillotine. What is its mysterious meaning? Tragically, it turns out to be something of a family curse, as each generation thereafter bears the same sign, which in turn leads to blackmail and murder.

Both Scotland Yard and an amateur American sleuth are tracking a master criminal known as The Frog. This moniker refers to the bulging-eyed mask worn by the evildoer, and is reflected by the frog icons painfully tatooed onto the forearms of his henchmen. The trail leads to the country manor of an enigmatic, steely-eyed nabob, whose repressed son has eyes for the artistes at the Lolita cabaret, and whose lovely daughter captures the fancy of both the American playboy and the villain himself. Murder, kidnapping and seduction ensue.

A man takes in three a dog and three runaway girls.