She is an iconic member of the British Royal Family, beloved for her beauty and charitable works, resented by her former husband and his mother, the Queen of England. But when a bomb explodes aboard her holiday yacht, British intelligence turns to one man to track down her killer: legendary spy and assassin Gabriel Allon. Gabriel is soon on the tail of Eamon Quinn, a master bomb maker and mercenary of death who sells his services to the highest bidder. But why would Quinn kill a member of the royal family and draw unwanted attention to himself? Quinn seeks the aid of Christopher Keller, a British commando turned professional assassin who knows Quinn's murderous handiwork all too well -- and the two are up against a cabal of evil with an intricate plan for revenge.