I have read none of the other Maggie Hope mysteries. I will need to add her to my list of novels to read. Following in the footsteps of Agatha Christie’s _And Then There Were None_. An author who used detailed research in preparation for a historical mystery has my admiration. Stuck in a Scottish castle with other British spies who have been deemed a threat to the British struggle in World War II, Maggie finds herself in a desperate search for a Nazi spy who is killing the “guests” one by one.