Stef promises Sariac a new hut for his birthday. Kantrop ends up hauling the stones for its construction on the flank of the mountain. To alleviate his burden, Pitt invents the wheel. But Kantrop's loads are doubled! Pitt, heartbroken, prefers to free Kantrop from this brutal exploitation. He lets Kantrop hide in the jungle, where the pterodactyl has to sharpen his survival skills. Meanwhile, Pitt realises the building site is a volcano about to erupt!