When they hear about the Dogs for Defense program, twins Charlie and Kate know their yellow lab Buster would be a perfect soldier dog. So they enlist Buster in the Coast Guard, where he works alongside Army horseback patrols to protect US shores from German U-boat attacks. Back home, Charlie and Kate discover a threat of their own--a coded message about a Nazi sabotage plan! With danger on every side, can Charlie, Kate, and Buster defend US shores from the Axis Powers?