Four-year-old Malone Moulin is haunted by nightmares of being handed over to a complete stranger and begins claiming his mother is not his real mother. His teachers at school say that it is all in his imagination as his mother has a birth certificate, photos of him as a child, and even the pediatrician confirms Malone is her son. The school psychologist, Vasily, believes otherwise as the child vividly describes an exchange between two women. Convinced that Malone is telling the truth, Vasile approaches police commander Marianne Augresse with the case, who has been searching for a gang of thieves that robbed a luxury store and left a couple dead in the neighboring town of Deauville to no avail. Marianne and her team soon discern that Malone's memory is in the hands of those around him; the cold members of the Moulin family and the people that they associate themselves with. With Malone's recollection of the past quickly fading to give way to pirates, animals, and other more innocent thoughts children have at his age, Marianne is desperate to find a through line. Well-crafted and showcasing the fragility of a child's cognition, The Double Mother is a riveting investigation to follow.