Lady Anne Ashburn and her father are at Seaford, a seaside resort, recovering from her mother's death. When the earl is called to Parliament in London, Anne becomes bored and explores nearby Singing Cave. Her maid is telling her tales of smugglers and the ghost who haunts the cave when they discover the body of a dead woman. By the time authorities go there, the body is gone, and no one believes Lady Anne. When her own attempts to discover the woman's identity are hindered by the local magistrate's disparaging remarks, she reaches out to Lord Ware.
Lucien, Viscount Ware, and his fellow agent Andrew Sherbourne are engaged in a secret inquiry for the Crown, hunting for a kidnapped young woman whose father is being forced to spy for France to keep her alive. Lucien would have gone to Seaford just to see Anne, but he and Sherbourne find it an odd coincidence that she has found a young woman...and they are looking for one.
What Lucien learns in Seaford nearly gets him killed and leads him and Lady Anne back to London. Another murder, a bounty on Lucien's head, a perilous ride in the park, an ambush, a mysterious note, and a very slippery French spy keep Lucien and Lady Anne busy searching for answers-and determined to catch a traitorous murderer before he gets away.