1882: London is in the grip of spirtualists and seances. Arthur Conan Doyle joins Dr Joseph Bell in a labyrinthine task of investigating a number of corpses found mutilated, floating in the River Thames. Their quest to uncover the architect behind the gruesome murders leads them through London's underground world of soothsayers and mediums. As the two sleuths probe deeper, they find themselves dangerously caught up in a 'spiritualism' darker and more terrifying than either man could possibly have imagined.