Flora Hansen calls herself a medium and makes a living by pretending to commune with the dead. But after a gruesome murder at a rural home for wayward girls, Hansen begins to suffer visions that are all too real. She calls the police, claiming to have seen a ghost, but ony one detective puts aside his skepticism long enough to listen: Joona Linna. Linna has spent more time at the scene of the crime than any other detective would. The case seems obvious on the face of it: one of the girls at the home escaped in the middle of the night, leaving behind a bloody bed with a hammer under the pillow. But why does Hansen insist that the murder instrument was a stone, not a hammer?