Two retired Texas Rangers, living in the small southern Texas town of Lonesome Dove, are told, by a returning old friend, of the huge opportunities to be had in the pristine lands of Montana. The driven and emotionally isolated Cal is determined to go, but Gus is only convinced when he hears that an old flame lives near to the route. So the two gather men, cattle and horses and set off on an epic cattle drive, encountering horse thieves, murderers, hostile Indians, inclement weather and a few inner demons.