After rescuing a lovely woman from an attempted robbery, Captain Lacey discovers that she is the widow of a colonel who'd been accused of murdering an English officer during the Peninsular War. Lydia declares that her husband was innocent and that she knows the true culprits' identities. Intrigued, Lacey, along with his friend, Lucius Grenville, begins to investigate. He soon finds himself mired in scandals of the past and surrounded by murders that are very much in the present.

On a cold January night in 1817, former cavalry officer Captain Gabriel Lacey is summoned to the banks of the Thames to identify the body of a young woman. When Lacey looks at the pretty, dead young woman, cut down too soon, he vows to find her murderer.

Captain Lacey stops to assist a young woman in the market at Covent Garden, and realizes to his astonishment that she is his daughter, Gabriella. Lacey then discovers that his estranged wife and her paramour, a French officer, have journeyed to London at the invitation of James Denis to dissolve her marriage to Captain Lacey.

A Bow Street Runner summons Captain Gabriel Lacey to a Berkeley Square ballroom where a young dandy was stabbed to death during a society ball. The prime suspect: Lacey's former commander, Colonel Brandon. Instead of denying the charges, Colonel Brandon allows himself to be arrested and claims, to Lacey's shock, that the lady he'd stayed protectively near at the ball is his mistress. Lacey realizes that he is the only person not convinced of Brandon's guilt - all present, including Brandon's wife, believe that Brandon committed the murder.

Captain Gabriel Lacey travels with Lady Breckenridge to his boyhood home in northern Norfolk only to discover mysterious happenings in and around the Lacey estate. A young woman, cousin of an old friend, has gone missing, strange objects appear in Lacey's ruined house, and the dark windmills on the marshes keep pulling Lacey to them.