Good-tempered engineer Johnny Munroe is blasting a railroad tunnel through the Andes for mine-owner Frederick Alexander, but frequent rockfalls hamper the work. Johnny falls for Alexander's daughter Maura; she encourages him, much to her father's dismay. Maura rebels against his stern control and sneaks away to meet Johnny. When they are stranded in the mountains and spend the night together, her outraged father insists they get married. At first they are very happy.
Alexander interferes with the supplies of timber, dynamite etc. in the hope of driving Johnny away, but his stubbornness keeps him there month after month. Frustration, worry and exhaustion affect his temper and destroy his marriage. When a friend is killed in another collapse, Johnny abandons the tunnel in favour of building a bridge to the mines. After Maura leaves him, he becomes increasingly bitter and reckless, alienating the workers.
At a formal Independence Day celebration, word comes that a flood is threatening the almost-completed bridge. As they struggle to finish the construction in the pouring rain the relationships between Johnny, his crew, his partner, his wife and her father are stressed.
This report prepared by Maureen Evans