A heartbreaking betrayal. A secret to uncover at any cost.

Bletchley Park, 1942. When teacher Hana Phillips is unexpectedly recruited to Bletchley Park she's determined to do her bit for the war effort. A talented linguist, she's soon put to work cracking Japanese naval codes and her newfound talents make her confidence soar, even as her work puts pressure on her already fracturing marriage.

Then Hana is tasked with a secret mission. There is a mole in her team, sharing secrets with the enemy, and Hana must search them out. There's no one she can trust, and she knows others - including her own father - have already been targeted for their attempts to find the spy. With the clock ticking, Hana must get to the truth - no matter the personal cost...