In a small village in northern France, Mathilde Weever is anxiously awaiting the return of her fiancé, Félix Mutin, who went missing during the final year of World War I. As the days turn into weeks, and the weeks into months, Mathilde's patience begins to wear thin. She receives a letter informing her that Félix has been killed in action, but she refuses to accept this notion, convinced that he is still alive. Undeterred by the skepticism of those around her, Mathilde sets out on a journey to find the truth about Félix's disappearance and presumed death. Along the way, she encounters a cast of eccentric characters who provide her with clues, misinformation, and insight into the brutal realities of war. As Mathilde delves deeper into the mystery, she discovers that Félix was part of a group of soldiers known as the " Blue Devils," an elite unit tasked with carrying out covert operations behind enemy lines. Her search takes her to the trenches of Verdun, where she meets a mute veteran named Bonnier, who becomes her unlikely ally. Through her relentless pursuit of the truth, Mathilde uncovers a web of lies, deceit, and tragedy that reveals the true nature of war and its devastating impact on those who fought it. Along the way, she also discovers unexpected things about herself, including her own strength, determination, and capacity for love. As the mystery slowly unfolds, Mathilde's quest becomes an act of defiance against the cruel fate that has befallen her fiancé. Through her unwavering dedication to finding the truth, she honors Félix's memory and proves that even in the darkest of times, the human spirit can endure and prevail.