Ginger Stuyvesant is a young American heiress, who moves to London to be with her aunt, and meets a British army officer. She and Captain Benjamin Harford become engaged, just in time for World War One.
Ginger and her aunt are both mediums, and in this very slightly alternate world, the British army recognizes a potential advantage. Ginger and her aunt become part of the "London branch," a corps of mediums and their supporting circles. British soldiers are conditioned, by a secret method, to report in to the mediums when they are killed in action. They can't pass beyond the veil until they've made their last report. This gives the British an often critical advantage.
The Germans don't have s similar corps because they still burn witches. They've realized something is going on, though, and are now trying to find the "conditioning" method, so they can have their own similar corps of, as they imagine it, ghost spies.
The "London branch" of mediums is in Le Havre. This is another vital piece of information the Germans don't have. They're not all that far from the front their dead soldiers are reporting in from.
When first an officer who was too persistent with Ginger, and then Captain Harford himself, are killed in circumstances Ginger knows are murder--because both men reported in to her--she's got a problem. General Davies doesn't believe the first officer's death was murder--he was drowned--and he's not going to assign her to investigate Ben's death.
But with Ben's ghost sticking around, telling her he'd discovered a traitor in their midst, but can't remember critical information, she has little choice. Gen. Davies won't believe her, but there's a traitor to be caught.
It's World War One. Some of their best mediums are West Indian. Some of their best soldiers are Indian. And both are undervalued by the British. Ginger, uncomfortably aware that she shared those attitudes not long ago, has had her viewpoint changed by working with those West Indian mediums. With her own circle, her aunt (also a medium), Ben's ghost, and Ben's batman, she sets out to find the traitor.
It's a nicely done wartime mystery, with their biggest but far from only problem being that they have no idea who they should trust and who they shouldn't. Ginger is smart, capable, and tough, but, medium or not, not superhuman. Ben's problems with remaining coherent become greater and greater as he stays on this side longer and longer, but he can't leave until he has "finished his business."
A very engaging tale. Recommended.
I received a free copy of this audiobook from Audible, in exchange for an honest review.