Gunner Peterson is a veteran dynamite man working for Jake and is romantically interested in Jake's daughter Mary. Johnny Brown, son of Nellie Brown who operates a boarding house, finds college too tame after his stint with a demolition squad in the army, and decides to quit. Getting a job with Jake, he is soon resented by Gunner when he tries to introduce some new methods and also starts showing an interest in Mary. A truck loaded with dynamite gets away from Hard Rock Mason and the loss of the truck causes Jake to have to borrow money from Nellie to keep his business going. Hard Rock is killed in a blast which Gunner decides was his fault, since he wouldn't listen to Johnny's ideas about how to set the charge, and he leaves. Later, when Johnny is testing charges, there is an unexpected blast and he is trapped in the tunnel.