In a small English village an elderly lady called Joan Stanley (Judy Dench) lives her years of peaceful retirement. One day she is arrested by the MI5 for being a Soviet spy and a traitor.
Joan has been hiding an incredible past: she was recruited by the KGB in the mid 1930s and became one of the most influential spies in living history. The adventure began when young Joan (Sophie Cookson), a dedicated physics student, fell intensely in love with a seductively charismatic Russian saboteur, Leo, who made her realize that the world might face a difficult situation in this mindless race to military supremacy. Knowing too well the devastating effects of bombs, she started working at a top secret nuclear research facility, and successfully transferred nuclear bomb secrets to the Soviet Union, which enabled them to keep up with the west in the development. Inspired by an extraordinary true story, Red Joan is an emotional story about sacrifice in the face of incredible circumstances.