November, 1843, and Agnes Bell (alter ego of Anne Brontë) is in Paris as governess to a French family. Her visit happens to coincide with a chess match at the Café de la Régence between the French Champion, Pierre St. Amant, and the Englishman, Howard Staunton. Little more than a quarter of a century after Waterloo, Anglo-French rivalry is still strong. For over a century French players have been acknowledged as the best in the world. Can Mr. Staunton bring that state of affairs to an end?
An onlooker at the match is murdered on his way home late at night. The case presents certain puzzling features, and the Sûreté take the unusual step of calling on unofficial help, including not only that of former criminal Eugène Vidocq, who operates on both sides of the law, but the far more scrupulous Miss Bell.
The result is her most distressing case yet, as the sickening murder of one of her employers brings her into contact with the dregs of the Parisian underworld. But aided by the perennially loyal Mr Tyrrell and two distinguished old soldiers from the Napoleonic War, Miss Bell yet again arrives at the truth, and ensures that justice is done.