The Codebreaker's Daughter by Myra L. Reynolds

Her father's death was ruled an accident. His last letter says otherwise.

When brilliant young cryptanalyst Evelyn Ashford is recruited to Bletchley Park in the spring of 1940, grief is the only thing she trusts herself to feel. Then she finally opens her father's final letter — hidden inside a cipher only she can break — and finds not a goodbye, but a warning. He believed a traitor was operating inside British intelligence. He gave the leak a codename. And the trail leads, impossibly, to the one person Evelyn has spent three years refusing to speak to: her own sister.

Margaret Ashford has secrets of her own — a double life inside the Foreign Office that she's never been able to explain, not even to the sister she loves. As the two women are forced back into each other's lives, they uncover a conspiracy that reaches into the highest levels of British intelligence, protected by a man both sisters have trusted since childhood. The closer they get to the truth, the more they risk losing — their careers, their safety, and each other, all over again.

For readers of historical fiction .THE CODEBREAKER'S DAUGHTER is a richly researched World War II historical novel of espionage, sisterhood, and the cost of secrets — set against the real, hidden world of Bletchley Park's codebreakers. Told through the alternating perspectives of two sisters on opposite sides of Britain's intelligence war, this is a story about the particular loneliness of carrying too much alone, and the courage it takes to finally put it down.

If you love your historical fiction with sharp intrigue, unforgettable women, and a betrayal you won't see coming, start reading THE CODEBREAKER'S DAUGHTER today.