World War 2 may be over, but for Danish twins Peter and Elise Andersen, the adventures are just beginning! Uncle Morten and Lisbeth return safely from Sweden, but the joyful reunion takes a tragic turn when an arsonist torches the Anna Marie, the family fishing boat. A number of menacing threats convince the twins that someone is out to destroy Uncle Morten for his work with the Danish Underground. But who? And why won't the adults take the warnings seriously? When Peter and Elise uncover a cruel plot to ruin Uncle Morten once and for all, they find themselves caught up in a frantic race to stop the culprit before he strikes again!