In 1665 England faces war with the Dutch and the capital is awash with rumors of conspiracy and sedition. As an experienced investigator, Thomas Chaloner knows that there are very few grains of truth in the shifting sands of the rumor-mill, but the loss of such an important warship and the murder of Paul Ferine, a Groom of the Robes, in a brothel favored by the elite of the Palace of White Hall makes him scent a whiff of genuine treason. As well as investigating the murder, Chaloner is charged with tracking down the leaders of a fanatical sect known as the Fifth Monarchists. He suspects his masters are not particularly concerned by their amateur antics, and that the order for him to infiltrate the group is intended to distract him from uncovering some unsavory facts about Ferine and his courtly associates. Then, as he comes to know more about the Fifth Monarchists and their meetings on High Holborn, he discovers a puzzling number of connections to both Ferine's murder and those involved with the defense of the realm.