During WWI, an injured and shell-shocked David Powlett-Jones applies to teach history at an English boys' public school, but he is concerned about whether a lower-class product of the Welsh mines can fit in. The boys are alarmed by his unconventional teaching approach and the masters suspicious of his
David goes home to Wales for the first time since he was invalided out, but his brother rags him about turning into an upper-class snob. He spends the day at the seaside and meets Elizabeth Marwood, a nurse who is also on holiday, and they agree to write. Back at school, students and masters celebrate the Armistice. David invites Beth to the school for Founders Day and pops the question.
Alderman Blunt wants to donate a war memorial to Bamfylde, but some of the Board resent a donation from a war profiteer. David and Beth marry and settle at Bamfylde, where Beth soon becomes pregnant. David fights the idea of a useless war memorial but loses to Carter and Blunt.
Headmaster Herries hires Mrs. Darbyshire, a semi-widow whose husband was gassed and will never leave the hospital, to teach second form. Beth gives birth to twin girls. A fire challenges David when he steps in as housemaster after Cordwainer is taken ill. Blades and Mrs. Darbyshire are drawn to each other.
When Cordwainer dies, Headmaster Herries offers David the housemaster position. Winterbourne, the son of a famous actress who is being divorced, runs away from school. While David supervises the hunt for the missing boy, Beth and the twins take the new car into town to get their pictures taken.
David is devastated by the death of Beth and the twins, and contemplates leaving Bamfylde for good. Years later, David discovers Carter has been calling his house the Kremlin and demands an apology. David runs into Julia in London and discovers she is interested in him.
Headmaster Herries announces his retirement, and David feels forced to campaign to be his replacement to be sure Carter can't turn the school into a military environment. David spends the night with Julia and proposes to her, but she reminds him she hates Bamfylde.
Alcock demands that the housemasters identify the older boys who have special friendships with younger boys. Carter intends to buy a prep school and invites David to be his partner. David is intrigued by Christine Forster, a would-be Labour MP from an upper-class background. Alcock threatens David with dismissal if he doesn't resign.
Headmaster Alcock is determined to have David fired and makes a formal complaint to the governors. David's book finds a prestigious publisher. Alcock tries to bribe Howarth with an assistant headmastership. Alcock reacts unexpectedly to the governors' decision.
David feels guilty about Alcock's death. Herries steps in as temporary headmaster to groom David to take over. David tries to encourage Christine, who is sure she is going to lose the by-election. David's book is published to glowing reviews.