Lady Violet Belmaine emerges from two years of mourning less than enthusiastic about resuming her place in Polite Society. She's talked into attending a country house party by her French physician friend, Hugh St. Sevier, only to find that the house party guests are preyed upon by a mysterious thief.

Among the guests is Sebastian MacHeath, Marquess of Dunkeld. Violet once considered Sebastian her closest confidant, but war and the passing years have changed him. Nonetheless, when Sebastian's valet, another veteran, comes under suspicion, Violet, St. Sevier, and Sebastian must work together to discover the true culprit, lest an innocent man be sent to the gallows for crimes he did not commit.