The year is 1757. On a bright June day, Lord John Grey emerges from his club, his mind in turmoil. A nobleman and a high-ranking officer in His Majesty's Army, Grey has just witnessed something shocking. But his efforts to avoid a scandal that might destroy his family are interrupted by something still more urgent: the Crown appoints him to investigate the brutal murder of a comrade-in-arms, who might well have been a traitor. Obliged to pursue two inquiries at once, Major Grey finds himself ensnared in a web of treachery and betrayal that touches every level of society - and threatens all he holds dear. From the bawdy-houses of London's night world to the drawing rooms of the nobility, from the blood of a murdered corpse to the thundering seas of the East India Company, Lord John follows the elusive trail of the woman in green who may hold the key to everything - or to nothing at all.