Rhys Lewis is the younger son in a poor family where the father is absent and the only source of income is what his older brother, Bob, earns as a coal miner.
He teaches himself English and the books he reads lead him to doubt the simplicity of his mother's faith; he is excommunicated from the Calvinistic Methodists after attacking Rhys's schoolteacher when he caught the latter beating Rhys, but continues searching for the truth whilst becoming active as a leader among the miners in their fight against an incompetent English supervisor who is badly mismanaging the mine to the detriment of the owners and workers alike.
After a workers' riot which he has tried hard to prevent, Bob is imprisoned on false charges; during his absence, the family declines into deep poverty.
Meanwhile, the English steward is fired and replaced by his Welsh predecessor, who is also a deacon with the Congregationalists, and who sees that the family is provided for and that Bob is reinstated on good terms when he comes out of prison.
Rhys and his mother are left without any income but are offered a home (and protected against Uncle James) by a simple-minded but generous cobbler called Thomas Bartley, a recent convert.
His best friend, Wil Bryan, leads him further and further astray until an incident where they very nearly kill a man brings Rhys to a crisis of conscience.
He eventually confesses his predicament to Abel Hughes who, instead of casting him out as he'd expected, treats him kindly and gives him good advice about how to find a true faith in Christ.
However, he feels he cannot accept the call because of the shame that his family bears due to the antics of his Uncle James and (he suspects) his father.
The experience is deeply traumatic, but clears the way for him to accept the call to the ministry and he pursues a short but successful career as a Calvinistic Methodist minister before dying relatively young from a wasting disease (very likely tuberculosis).