10 Marchfield Square follows Celeste Van Duren, an eccentric elderly heiress who created her London apartment building as a refuge for people in need of a fresh start. When one of her tenants is murdered and his wife becomes the prime suspect, Celeste recruits two unlikely investigators—a warm-hearted cleaner who knows everyone's secrets and a cynical failed crime writer who barely knows his neighbors—to uncover the truth. As they dig into the victim's shady dealings in the art world, they discover that the greatest danger may be hiding much closer to home.