Set in the stunning and varied Canadian landscape, it tells the story of six members of a Nazi U-boat crew, stranded on land when their vessel is sunk by patrol planes. Their mission is to return to Germany, via the neutral U.S., and follows their attempt to reach the border, the eponymous 49th Parallel.

Along the way they try to spread their Nazi ideology, which falls on stony ground. Lawrence Olivier, Leslie Howard and Eric Portman lead the cast and with an atmosphere made all the more rousing via the score composed by Ralph Vaughan Williams.