I really enjoyed
The Alice Network by Kate Quinn. It was an engrossing read that sticks with you after it's over.
The Alice Network weaves narratives from WWI, WWII, and post-WWII France and England.
In 1947, Charlotte St. Clair (Charlie) is a wealthy but adrift American. At nineteen, she has flunked out of college and is pregnant. Her parents intend to have her Little Problem dealt with in Europe. Charlie, however, decides to track down the last person to have heard of her French cousin Rose, who disappeared in 1944. All Charlie has is a name, Eve Gardiner.
In 1915, Eve Gardiner was recruited to join a network of female spies operating in German-occupied France. Eve joins the Alice Network, which was run by the "Queen of Spies" Lili (Code name Alice Dubois). For two years, Eve (Code name: Marguerite Le Francois) works side by side with her fellow "fleurs du mal"* Lili and Violette. Eventually the Alice Network is discovered and Lili, Violette, and Eve are captured, tried, and imprisoned. *For those who enjoy it, Baudelaire's
Les fleurs du mal features in the novel.
Though she survives, Eve is haunted by the betrayal that led to the Alice Network's downfall. The brazen young Charlie helps Eve seek revenge and the two discover a link between Eve's spy work in WWI and her cousin Rose in WWII.
The Alice Network is based on true events and historical figures. The real "Queen of Spies", Louise de Bettignies took the code name Alice Dubois ran one of WWI's most successful spy rings in Lille and the surrounding area. Violette is based on Leonie Van Houtte who worked closely with Louise de Bettignies. Eve Gardiner is a fictional character, but her code name Marguerite Le Francois is based on an actual incident in Louise's life.