A series of baffling murders among a group of imprisoned agents threatens the outcome of World War II in this chilling mystery from the New York Times bestselling author of Mr. Churchill's Secretary.

November, 1942. World War II is raging, and former spy Maggie Hope knows too much: what the British government is willing to do to keep its secrets, who is lying, who the double-crossers are. She knows exactly who is sending agents to their deaths. These are the reasons Maggie is isolated on a remote Scottish island, in a prison known as Killoch Castle. When one of her fellow inmates drops dead in the middle of his after-dinner drink-he's only the first. As victims fall one by one, Maggie will have to call upon all her wits and skills to escape-not just certain death . . . but certain murder. For what's the most important thing that Maggie Hope knows? She must survive.

Praise for The Prisoner in the Castle

"The colonel sums it up best on page ten: 'If you take a pretty girl and teach her how to kill, it can cause problems.' Not just problems-electrifying action and nonstop surprises. I loved this book!"-R. L. Stine, author of the Goosebumps and Fear Street series

"Another literary tour de force . . . From the book's perfectly calibrated plot to its incisively etched characters, everything is handled with perfect finesse by the author."-Poisoned Pen Newsletter

"One pleasure of a mystery series is connecting with a character that changes and grows with each novel. . . . Maggie's intelligence and loyalty to the war effort continue to evolve in [Susan Elia] MacNeal's series. . . . Solid twists keep the plot of The Prisoner in the Castle churning until the surprise finale."-Associated Press

"A mystery . . . tailor-made for readers in the post-election, #MeToo era. . . . If you love a tricky puzzle that requires you to keep track of multiple alibis over time, this is your summer read."-The Washington Post

"Evocative."-Publishers Weekly

"MacNeal uses [Agatha] Christie's And Then There Were None as a framework for a character-driven mystery/thriller that successfully emulates the original."-Kirkus Reviews