Seeking shelter from a pounding rainstorm in a remote region of Wales, several travellers are admitted to a gloomy, foreboding mansion belonging to the extremely strange Femm family. Trying to make the best of it, the guests must deal with their sepulchral host, Horace Femm and his obsessive, malevolent sister Rebecca. Things get worse as the brutish manservant Morgan gets drunk, runs amuck and releases the long pent-up brother Saul, a psychotic pyromaniac who gleefully tries to destroy the residence by setting it on fire.