In 1657 the government prepares for a foreign invasion expected on the Medway. Luke is sent to uncover the local Royalists who might support the incursion. He is appalled at the dysfunctional nature of the household of the government's strongest supporter where he is confronted with several attempts on his life and a series of murders. He must find the murderers, identify the traitors- and a mysterious agent exacting Lady Mary's revenge.