"Who does the mysterious ship hidden behind the waterfall belong to? To answer this question Leonardo and his friends head to the galleon and climb aboard. Just as they hide behind some barrels, a band of pirates appears! Corsair Grey and his crew reveal their plan to go to the monastery and find the treasure "... and whoever took the parchment before us will come to a bad end!" one of them adds menacingly.
Meanwhile, Laura, Gottardo and the three Brandis continue to follow Leo's movements from afar: once they reach the ship they are captured by the river pirates and reveal to Corsair Grey that they are trailing Leo and want to get to the treasure before he does.
Our heroes realise that an eagle claw is engraved on the handle of the key found in the cave. This clue leads them to think that the treasure they are searching for could be on Ibex Peak. With the help of his flying machine, Leo and his friends reach the top of the mountain and find a sheet of copper with a maple seed engraved on it: what could this mean?
Meanwhile, the Brandis, instigated by Laura, try to recreate Leonardo's flying machine, with disastrous consequences...