The French Girl by Catherine Law

A secret, a sacrifice, and a scandal...
Summer 1939 - When war breaks out, Sylvie is marooned with her cousin Nell's family in the Chiltern hills and cannot return to her Normandy home.
During the early days of rationing, blackouts, and the threat of bombers in the skies, Sylvie and Nell have to grow up quickly. Yet as the war rages around them, it's the competition and jealousy between the two that dominates their lives.
When the girls fall in love with the same man, their relationship is truly tested. But the war pulls them all apart and changes the course of their lives - until their secrets are revealed, with devastating consequences.
A heartbreaking story of love and hope, secrets and lies. Perfect for fans of Kathryn Hughes and Leah Fleming.
Previously published as The September Garden.