'The Underground Library' unfolds against the backdrop of World War II in London, where the future of Bethnal Green Library hangs in the balance under the Blitz. Assistant librarian Juliet Lansdown strives to transform the library into a critical community hub despite gender bias and personal struggles. Alongside her, Katie Upwood grapples with loss and a profound secret, but finds solace within the books' embrace. Sofie Baumann, a Jewish refugee, seeks refuge and her lost sister amidst the chaos. When their sanctuary is shattered by bombs, Juliet channels her resolve into relocating the library to an Underground station, offering an oasis of stories amidst the nightly bombings. Each woman must navigate their tribulations to preserve this vital heart of the community.