Deep within the cavern-riddled chalk cliffs above the English Channel there brews a threat to the very sanity of the people of Britain. A startling madness infects the members of the Explorer's Club in London, the debacle coinciding with the disappearance of Alice St. Ives and the murder of the lighthouse keeper at Beachy Head. Langdon St. Ives sets out to rescue his wife and to stop the accelerating train of events hurtling he and his friends into a dark tunnel of madness and death.