The French Medium - a Nat Frayne mystery

In Victorian London the French Mesmerist Madame Davignon claims to unite the bereaved with the spirits of their loved ones. A simple enough swindle. To start. But when the game mounts first to blackmail, then murder, Detective Inspector Nat Frayne poses as a client, hoping to entrap the medium. Instead, the hunter becomes the hunted when she unites him with the spirit of his lost wife. Illusion. It must be illusion.
Yet he cannot tear himself away.