The days of slaughtering buffalo were supposedly over, mainly because there were so pitifully few of them remaining. But with top dollar on offer for their severed heads as trophies, some hunters just can't resist. In Yellowstone Park, where such poaching is illegal, Captain Moses Harris and his company of US Cavalry are assigned the job of stopping them. Yet in the depths of winter, following an apparently motiveless murder on the army post in Mammoth, the captain begins to realise that it is not just the buffalo that are threatened by greed and corruption. With a merciless hired gun on the loose, Harris sends army scout Deke Wilson and a squad of soldiers in pursuit. This triggers a sequence of events involving high finance and the Northern Pacific Railroad, which not only endangers the lives of them all, but also the very survival of America's first national park.