In London in 1816, aristocrat Marcus Toole is burned alive on a hill used by neo-Druids. Sebastian's nephew Bayard was with him before the attack but claims to remember nothing, leaving Sebastian and Hero to determine whether he is a witness, a target or part of the crime.
Two more members of Bayard's circle are killed in scenes designed to resemble ancient Celtic sacrifices. The trail leads through highwaymen, radical politics, journalism and the victims of privileged young men, suggesting that the ritual imagery disguises a campaign of revenge that could intensify the unrest gripping the city.