While escaping the apocalyptic floods and earthquakes that are sweeping across the earth, Martin Webster is separated from his wife Helen and children, Ronny and Mary Ann, and is stranded on a newly formed island, located somewhere near the now devastated New York City. At the same time, Claire Arlington, a champion long-distance swimmer, is found unconscious on another island by two ruffians, Norwood and Jephson, who carry her to their cabin. Months later, after Norwood and Jephson begin to fight over her, Claire flees from the men and swims toward Martin's island. Although followed by Jephson in a boat, Claire reaches the island's shore safely, then collapses with exhaustion. Martin, who has secreted a load of supplies in a tunnel, takes Claire to his cabin and nurses her back to health. When Jephson finally arrives on the island, he stumbles onto Martin's tunnel, then runs into Bellamy and his gang, thugs who also inhabit the island. Still determined to find Claire, Jephson tells Bellamy's gang, who had been driven from a nearby village for raping and stealing, about the tunnel and his missing "woman." Unknown to Martin, Ronny, Mary Ann and a sickly Helen are being cared for in the village by Tom, the unofficial village leader. In spite of Tom's urging that she marry, Helen refuses to accept Martin's death and turns down Tom's proposal. Martin, however, falls in love with Claire and, assuming that Helen is dead, makes her his common law wife. Eventually Jephson discovers Martin's whereabouts and, after a brutal fight, abducts Claire and takes her to the Bellamy hideout. As Jephson is about to rape Claire, Martin sneaks into the Bellamy camp and rescues her. Martin and Claire then hide in the tunnel but are followed there by Jephson and the gang. In an attempt to force the armed Martin and Claire out of the tunnel, Jephson orders that a fire be lit at the tunnel's entrance. When the couple remains in the tunnel, Jephson enters and, while fighting Martin, is killed with a spiked club by Claire. At the same time, Tom and a band of vigilantes track the gang to the tunnel and bring Martin and Claire to their village. There, Martin reunites with Helen and confesses to her his relationship with Claire. To deal with village unruliness and greed concerning the distribution of goods, Martin organizes an auction and establishes an effective monetary system for the community. After Martin is elected "mayor" by the townspeople, Claire, who has declared to Helen that she cannot give up her common law husband, swims out to sea.