Aylwin Hundrych is a diplomat with political aspirations, who was once involved with a French girl, Antoinette, with whom he unwittingly shared details about a royal visit to Paris - details which put the King's life in danger. Antoinette's brother holds the former lovers' letters, and is threatening to use them. Hundrych makes a first payment, but the demands continue.
Hundrych enlists his old friend Sir Vane Tabbard's son, an ex-commando called Gray Tabbard, who is not too scrupulous about what he does. Gray searches the blackmailer's apartment, but reports back that he cannot find a particularly compromising note.
And Gray is in love with the girl Hundrych plans to marry . . .