While winging their way to Denmark the Happy Hollisters become friendly with a member of the Queen of Denmark's staff. She is bringing home the Queen's own valuable reproduction of the "Little Mermaid," the famous statue that overlooks the harbor in Copenhagen. While she is showing the Hollisters the little figurine, another passenger expresses interest in seeing this rare treasure. His interest, however, strikes the five Hollister children as being more than just enthusiasm for the beauty and workmanship of the figurine. In the excitement of preparing to land at the Copenhagen airport, he is forgotten until, upon landing, the figurine is found to be missing. From then on the Hollisters find themselves becoming more and more involved with the strange man with the beard and his rather peculiar activities. Much to the Hollisters' surprise they find not only is the figurine an object of mystery, but the trail of the bearded man is leading them to a ring of international thieves and their search for a bejeweled treasure, hidden centuries ago. The Hollisters finally discover a clue to this treasure from the study of the history of the ship models hung in the churches of Denmark to honor lost seamen.
