While war ravages the city above her, Clara Dutton has risked everything she holds dear to turn London's Bethnal Green tube station into the country's only underground library. Along with her best friend and assistant Ruby Munroe, Clara ensures the library is the beating heart of life underground. But as the war drags on, the women's determination to remain strong in the face of adversity is tested to the limits when it may come at the price of keeping those closest to them alive.