Set against the backdrop of World War I, this mystery novel mixes elements of espionage, the supernatural, and the classic whodunit. The story unfolds on an isolated island, where Lord Highmount has decided to host a gathering at his mansion, Blackwater Abbey, bringing together an eclectic mix of individuals, including soldiers, spiritualists, and family members.

Among the guests are Kate Cartwright and Captain Robert Donovan, two individuals with unique abilities to perceive the supernatural. Kate, in particular, has been well aware of ghosts for much of her life, a trait that sets her apart and lends her a unique perspective on the strange occurrences at Blackwater Abbey. Lord Highmount, intrigued by spiritualism, aims to contact his two sons who were lost to the war, seeking closure and answers from the beyond.

However, as the story progresses, it becomes apparent that there are more tangible threats than ghosts lurking in the shadows of Blackwater Abbey. Espionage and hidden agendas come to the fore, as Kate and Donovan find themselves entwined in a web of intrigue and danger.