Tintin is not the only one who knows the secret of the parchment hidden inside the ship's mast. The Byrd Brothers, antique dealers, also find a copy of the model ship Unicorn in their basement. They also start looking for the other two parchments, and they are not really the friendly kind. When their agent, Barnaby, tries to warn Tintin about the Byrd Brothers they try to kill him and also kidnap Tintin to find out about the parchments that they are missing. At last the parchments are recovered and the mystery solved.