Our woman in Moscow / Beatriz Williams.

In 1948, Iris Digby vanishes from her London home with her American diplomat husband and their two children. Four years later, Ruth Macallister receives a postcard from the estranged twin sister she hasn't seen since 1940. Since that one catastrophic summer in Rome, as war was engulfing Europe and Iris was falling desperately in love. Within days, Ruth is on her way to Moscow, posing as the wife of Agent Fox in a precarious plot to extract her sister from behind the Iron Curtain. But the truth behind Iris's marriage threatens to unravel everything, and as the sisters race to safety, a dogged Soviet KGB officer forces them to make a heartbreaking choice.