In an English mining town during the 1870s, Joan Lowrie falls in love with Fergus Derrick, the new chief engineer who vows to improve working conditions. Joan's father Don, however, runs the mine and likes conditions just as they are. As a result, he quickly learns to detest the crusading Fergus, even to the point of trying to murder him. Joan saves Fergus, after which Don is killed by one of the workers whom he habitually mistreated. Don's death removes the only impediment to Joan's romance as well as to improvements in the mine, so while Joan and Fergus make plans for their marriage, plans also are developed to make the mine safer and more efficient.—Anonymous

In the Lancastershire coal mines women work above ground, handling and disposing of the coal that their men dig from below and send to the surface. This work creates a type of self-reliant and sometimes conspicuously rugged female, born to labor and bred to the hard task of manual toil. Old Man Lowrie has grown to be the bully of the village; his daughter, like all her kind, works by day and keeps his home as best she can. The "Lass" secretly loves the chief engineer of the mines, and he is attracted by her rugged beauty. There is trouble in the mines because the precautions against the explosion of "fire damp" are continually violated by Old Man Lowrie. After vainly attempting to enforce compliance with the rules, the chief engineer takes the matter of discipline into his own hands and in a fistic encounter subdues the recalcitrant Lowrie, but stirs his vengeful hatred. Incident to the troubles at the mine, the rich owner sends his milk-sop son to gather an idea of conditions, but the only idea the fop puts into operation is to lure from home a frail girl of the village, by his promise of fine clothes and easy living. Running through the story is the rector's daughter, a refined young girl who busies herself with missionary work among the villagers. It is this girl who untangles the threads and serve to make pleasanter the path of love for the "Lass" and brings solace to the deserted and disgraced daughter of the mines, who is forced to come home for shelter when the villain in the piece has cast her off. Old Lowrie, licked but vengeful, attempts to murder the engineer of the mine who had conquered and humiliated his bullying spirits. He attempts to waylay the engineer, but "The Lass" thwarts his purpose. In a later attempt she is not so completely successful, but in a struggle of strength Lowrie manages, by felling his opponent with a heavy stone, to severely injure the engineer. The stay in hospital of the wounded man serves to ripen his attachment for "The Lass" into perfect love, and the rector's daughter takes the girl of the mine in hand to educate and fit her to be the wife of the engineer. Meanwhile the love affair of the "little missionary" goes on apace and ends with the "happy ever after" outcome that ends all good love stories.—Moving Picture World synopsis