The first part of the trilogy focused on the mysterious actions of Sandrine and Claudine, two sisters bent on avenging their father, who had been falsely accused of collaboration during WWII and murdered by dishonorable résistants. At the same time, Sandrine's baby, who was fathered by a German officer, was abducted and presumably entrusted to foster parents, leaving the mother deeply distressed.
The second book, also set in 1947, is about the search for the missing child. Private eye Toni Bonnet is determined to return him to his grieving mother, but locating the foster parents proves difficult. Led by clues that point to the involvement of former Spanish underground fighters who had served in the French Résistance, Bonnet travels from Paris to the Eastern part of the Pyrenees, where half a million Spanish Republicans had sought refuge after Franco's victory in 1939. While the action in Two Sisters revolved around the murders of French Résistance heroes, the historical backdrop of The Child shifts to the Spanish Civil War.
