The Citadel was a groundbreaking novel of 1937, based by Cronin on his own experiences as a doctor in the Welsh coalfields. Nye Bevan, the post war Labour Minister who implemented Britain’s National Health Service stated it had a profound impact on him.

In October 1924, Andrew Manson, an idealistic, newly qualified doctor, arrives from Scotland to work as assistant to Doctor Page in the small Welsh mining town of Drineffy . He quickly realises that Page is unwell and disabled and that he has to do all the work for a meagre wage.

Manson works to improve matters and receives the support of Dr Philip Denny, a cynical semi-alcoholic. Manson marries Christine Barlow, a junior school teacher and the three between them fight to improve the lives of the local miners, not without opposition from interested parties, not least the leading doctor in the area.