Franklin is enjoying summer vacation when his family receives a rare visit from Aunty Lucie, an archaeologist with a passion for treasure hunts.
Franklin’s grandmother remembers her own treasure, a box that she’d buried when she was a little girl… But during this evocation of the past she suddenly falls ill.
Franklin and his friends decide to find this box that could save Granny. Aunt Lucie accompanies them on this expedition deep into the forest, along with Samantha, her goddaughter, whose abrasive temperament upsets the group’s equilibrium.
Franklin must summon up all his patience to keep the young explorers fixed on their objective.