At the request of Her Majesty’s government, private enquiry agent Cyrus Barker agrees to take on his least favorite kind of assignment—he’s to provide security for a secret conference with the French government. The conference is to take place on the private estate of Lord Hargrave on a remote island off the coast of Cornwall. The goal of the conference is the negotiation of a new treaty with France. The cover story for the gathering is a house party—an attempt to introduce Lord Hargrave’s two unmarried sons to potential mates.
But shortly after the parties land at the island, Lord Hargrave is killed by a sniper shot, and the French ambassador’s head of security is found stabbed to death. The only means of egress from the island—a boat—has been sent away, and the means of signaling for help has been destroyed. Trapped in a manor house with no way of escape, Cyrus Barker and his assistant, Thomas Llewelyn, must uncover which among them is the killer before the next victim falls.
Godolphin Island, one of the Scilly isles off the tip of Cornwall, provides the isolated setting for Thomas's uneven eighth Victorian mystery (after 2015's Anatomy of Evil). Private detective Cyrus Barker and his sidekick, Thomas Llewelyn, set out for the island at the request of Lord Hargrave, who works for the Royal United Service Institution, which monitors other countries both politically and militarily. Hargrave is to meet with the French ambassador on Godolphin Island to try to resolve tensions between Britain and France over their respective African colonies. To keep the meeting secret, Hargrave has arranged a house party at his estate, and he retains Barker and Llewelyn to provide security for the ambassador. But soon after the detectives' arrival, a sniper fatally shoots Hargrave, and more shooting deaths follow at regular intervals. Despite the dramatic setup, Thomas fails to build much suspense, largely because there are numerous victims with only sketchy personalities. Many readers will identify the culprit early on.