Zane Grey is at his best in this story of the building of the Boulder Dam, later renamed the Hoover Dam.

Straddling the great Colorado River, a huge structure is slowly rising-a dam that will alter the course of this ravaging river and harness its awesome power. Men from all over America have flocked to the site, laboring at the dam by day and filling the nearby Las Vegas gambling houses by night.

To Lynn Weston, a rich man's son, working on the dam means independence and the chance to prove his courage. But an even greater challenge faces Lynn: he discovers a girl who has escaped her abductors in the back seat of his car and becomes her self-appointed protector. Suddenly, he finds himself threatened by a pack of ruthless gangsters with a vicious plan to blow up the dam.