It is June 1940 and fifteen-year-old Olivia Baldini's idyllic English life is shattered as Britain declares war on Italy. With hyperthymesia, Olivia possesses an extraordinary ability to recall information with vivid detail, a gift that makes her invaluable to Churchill's secret sabotage army, the Special Operations Executive (SOE). Trained in nursing, coding, and espionage, Olivia is dispatched behind enemy lines in Italy, aiding partisans and resistance fighters.

Nino Fabris, dreaming of world travel with the merchant marines, is thrust into the war when his ship is conscripted. Captured in North Africa and sent to a POW camp in Kenya, Nino seizes a chance for freedom by joining the SOE.

In the chaos of war, Olivia and Nino's paths intertwine. The Cipher is a gripping tale of love, resilience, and the power of the truth — and who you trust with it.