The Citadel follows the life of Andrew Manson, a young and idealistic Scottish doctor, as he navigates the challenges of practicing medicine across interwar Wales and England. Based on A.J. Cronin's own experiences as a physician, this book boldly confronts traditional medical ethics, and has been noted as one of the inspirations for the formation of the National Health Service.

This story has been adapted into several successful film, radio, and television productions around the world, including the Oscar-nominated 1938 film starring Robert Donat, Rosalind Russell, Ralph Richardson, and Rex Harrison.

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