A lawman in search of America's most notorious train robbers finds himself in the recently deserted town of Purgatory. He soon finds out that what hides in the shadows is so much worse than the men he's hunting. In the wee hours of the morning on the great plains of a country still reeling from the Civil War, Yankee Lawman, Beau Riffen and his Tracker, ex-confederate, Cody Parnum are attacked by something so frightening it shakes them to the core. With their horses gone, they walk for miles over desolate terrain until they finally come upon the small town of Purgatory. Looking for relief, they find the unthinkable. The entire town has been recently abandoned. The only signs of life they find is an African American trapper that claims he arrived the night before and a prisoner in the stockade that has seen better days. What happened? Where did everyone go? The answers will come to them in the form of an ancient evil that waits in the darkness hell bent on revenge. In order to survive this disparate crew must learn to trust each other and figure out just what happened. The only clue they are left with is the name "Yee Naaldlooshii," or " The Skinwalker."