Colin and Céline’s parents manage an undertaker’s company. Quite busy with their work, they don’t have much time for their kids, who are teased because of their parents’ profession. Their schoolmates constantly make fun of them, calling them "Grave Diggers" or "Cold Cooks." As a result, the lonely twins get into mischief and end up getting suspended from school for two days. Fortunately, they can rely on Poussin, the gravestone engraver, who loves drawing and telling them stories. One day, Poussin directs their attention to a strange marking on a grave...