"Citadel" is a novel written by the English writer Ai. J. Cronin. The book tells the story of a young doctor who strives to change the medical system in a small town. The main character, Andrew Mendl, faces corruption and difficulties in career growth, but desperately fights for his principles. "Citadel" is a reflection of complex moral issues, eternal affairs and internal struggles that accompany everyone who tries to change the world around them. This book leaves deep thoughts about our values, dreams and struggle for justice.