 Gunner Peterson (William Gargan) is a veteran dynamite man working for Jake (Irving Bacon)and is romantically interested in Jake s daughter Mary (Virginia Welles.) Johnny Brown (Richard Crane), son of Nellie Brown (Mary Newton) 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 (Frank Ferguson)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.