Set during the thrilling social change of the mid-1950s, these new episodes capture the lives of four remarkable women with extraordinary intelligence, breath-taking capacity for pattern recognition and an ingenuity for decryption.

The series follows two of the original lead characters, Millie (Rachael Stirling, Churchill's Secret) and Jean (Julie Graham, Shetland), as they travel to America and join forces with US codebreakers Iris (Crystal Balint, The Good Doctor, Prison Break) and Hailey (Chanelle Peloso, Zapped, Incredible Crew) to tackle a string of new murder cases. Using their unique skills and intellectual abilities, the four women solve complex mysteries that baffle local law enforcement.