Lt. Col. Glenn Manning is inadvertently exposed to a plutonium bomb blast and although he sustains burns over 90% of his body, he survives. Then he begins to grow, but as he grows he starts losing his mind. By the time he stops he is 50 ft tall, insane and is on the rampage.
Kay Parrish, a society girl, finds she is penniless when her father dies. However she persuades Terry Gallagher to give her a hostess job at his New York City clip-joint, which he operates on the theory that if the suckers want it he'll give it to them, albeit he does apply some principles regarding the matter. A Broadway playboy, Greg Emerson, falls in love with Kay and proposes but his high-society parents object strongly. Terry. although he also has fallen in love with Kay and doesn't realize she feels the same about him, sets out to provide a happy ending for the couple.
Soapy Gibson (Edward Ellis) and his wife Annie (Marjorie Rambeau) run a lonely hearts club in a small town. Even during the Depression years these were often "clip joints" - places where people with money but no mate got taken by someone offering the promise of companionship. However, Soapy and Annie are strictly on the level - and they have more than one reason to want to stay on the level. You see Soapy escaped from the law years ago, had some plastic surgery and changed his name, and has been living on the lam with his wife ever since.
Fate brings a job at Boulder Dam and romance with a saloon singer into the life of a young man on the run.
The plot revolves around a rivalry between sand-hog "Hard Rock" Harrigan (O'Brien) and his foreman Black Jack Riley. At the center of their conflict is their mutual affection for heroine "Andy" Anderson (Irene Hervey). But when the chips are down and Riley is trapped in a tunnel cave-in, it is Harrigan who comes to the rescue.