World-famous English astronomers Charles Mason and Jeremiah Dixon come to the American colonies to survey the disputed boundaries between Pennsylvania and Maryland. To settle the long-standing and often-bloody border dispute once and for all, the two scientists transport cutting-edge and fragile surveying equipment through hundreds of miles of rugged wilderness. For nearly five years, the expedition endures treacherous weather, deadly terrain, and the constant threat of attacks by hostile Native American tribes. Against all odds, they complete the survey with pinpoint accuracy, and their Mason-Dixon Line helps to bring peace to the new frontier.