When a bomb explodes aboard the yacht of an iconic member of the British royal family, Gabriel Allon 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? Allon 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.