London, 1816: When a notorious young aristocrat is burned alive on a windswept hill popular with neo-Druids, former cavalry officer Sebastian St. Cyr, Viscount Devlin, finds himself plunged into a murder investigation shadowed by tales of ancient human sacrifices and long-buried secrets. The victim, Marcus Toole, was the only son and heir of a prominent nobleman. His closest friend-Sebastian's own nephew, Bayard-claims to have passed out drunk before the attack and remembers nothing. But when Sebastian and his brilliant wife, Hero, delve deeper into the sordid activities of Bayard and his friends, they come to realise that Bayard may not be as innocent as he pretends. Following a tangled trail that leads from a disaffected former soldier-turned-highwayman to a beautiful, courageous journalist and a Jamaican-born fencing master with ties to a radical political movement, Sebastian begins to suspect that Bayard and his friends are being targeted in revenge, by victims who believe they have no other recourse. Then two more of Bayard's friends are killed, their murders staged to echo the ritual sacrifices of the ancient Celts. With the palace shaken by the fear of riots and one horrifying death following another, Sebastian must race to stop a ruthless plot that threatens the lives of innocents and could rip his troubled nation apart.