The first four episodes from the spin-off series of the ITV drama following a group of former World War II codebreakers as they attempt to make use of their skills in their post-war lives. In this series, with the team no longer together, Jean (Julie Graham) is becoming restless in her life as a librarian and Millie (Rachael Stirling) is fed up of her tutor work with upper-class children. With a San Francisco murder capturing the attention of the girls, they make the bold decision to take to the US to utilise their unparalleled skills once more where they meet Iris (Crystal Balint) and Hailey (Chanelle Peloso), their American equivalents. Can the four women solve the murder case together? The episodes are: 'Presidio', 'Wake', 'Charlotte's Web' and 'Madhouse'.