A mysterious, man-sized monster kills a fisherman at sea. A Biologist and a Federal Agent discover a man's body, washed up on the beach and covered with radiation burns.

A gun hand named Lane (John Wayne) is hired by a widow (Ann-Margret), Mrs. Lowe, to find gold stolen by her husband so that she may return it and start fresh.

There’s a deficit of good, honest women in the West, and Roy Whitman wants to change that. His solution is to bring a caravan of over 100 mail-order brides from Chicago to California. It will be a long, difficult and dangerous journey for the women. So Whitman hires hardened, cynical Buck Wyatt to be their guide across the inhospitable frontier. But as disaster strikes on the trail, Buck just might discover that these women are stronger than he thinks.