The novel begins with the organization of an expedition to rescue Bowen J. Tyler, Lys La Rue, and the other castaways marooned on the large Antarctic island of Caprona, whose tropical interior, known to its inhabitants as Caspak, is home to prehistoric fauna of all eras. Tyler's recovered manuscript detailing their ordeal is delivered to his family, and the relief effort is put together by Tom Billings, secretary of the Tyler shipbuilding business. The expedition's ship, the "Toreador", locates Caprona, and while the bulk of the crew attempts to scale the encircling cliffs Billings flies over them in an aircraft.