Pit Poirot against peril and you get perfection. Someone is stalking the lady of End House. She claims her only friend is a ghost. Hercule Poirot has his more earthbound theories of what's happening.
An emaciated stranger approaches Hercule Poirot, shouts a warning about "the big four" and drops dead. Who knew Poirot's inquiry into the man's odd behavior would lead to an underground laboratory, an
