In mid-1944, a half-million German prisoners of war are working in U.S. factories and fields because military enlistments and the draft have caused labor shortages. Two hundred PWs are billeted in an old Civilian Conservation Corps camp on Muskrat Island in the Minnesota River at New Bonn.Twelve-year-olds, Frank Warner, Jack Steiner, and Skeeter Stark stake out the PW camp from an abandoned cabin along the river. Franks and Jacks dads are serving with the 3rd Infantry Division in Italy. Skeeters brother is an Army Ranger in France.Frank and Jack are Boy Scouts, and fluent in Morse Code; however, a series of mysterious radio messages intercepted in that format baffles them.The boys build a raft, land on the island, and encounter a PW who drops a matchbook cover with the following strange words and numbers printed on the back: KAISER BRIGHTMAN 082314. The trio is dawn into a Nazi conspiracy of murder and sabotage that imperils many lives, including theirs.