Traveling through Europe in the summer of 1901, Mandie and her group arrive in Antwerp, Belgium, where they plan to visit art museums as well as do sightseeing around the beautiful city. Mrs. Taft has made it clear that there are to be no more adventures like, Mandie, Celia and Jonathan have gotten involved with in France, Italy, Switzerland, and Germany.

But what are Mandie and her friends to do when adventure discovers them? Who would believe that a seemingly abandoned fishing boat has strange sounds coming from inside? Until they find out more, should they tell Mrs. Taft?

And what is the link between the boat and the suspicious man they think has stolen the priceless painting from the art museum?

Who is the bearded giant?