No respite for Cap-de-Roue, PÔetard-ßa-mßeche and Tarzan: now another case falls on them! Someone found the tree their cabin is built in and left a sack full of acorns there. The boys won't let anyone conquer their territory so easily! Certain that the intruder will come back for a walk around the area, they decide to spend the night in the cabin. What they are far from suspecting is that the ranger may not be quite ... human! In Saint-Trop-Loin, there is talk of a gorilla who escaped from the zoo in the neighboring town. Is there a link between the animal on the run and the creature seen by the guys? When Tarzan's carrot and peanut butter farts and the resounding burps of Cap-de-Roue and Firecracker aren't enough to scare the disturbing critter away, Jordane decides to get involved. Will his ingenuity allow them to elucidate this new mystery?