Two drunk men are out in the woods, poaching deer, when one of them is attacked and killed by a tree-like figure. His friend panics and flees, only to crash his vehicle.
Team Grimm attempts to figure out what the meaning is behind the skull-faced thing that attacked Eve from the mirror. Diana informs them that it is in some other place and that it hasn't happened yet.
Nick, Hank, and Wu investigate the poacher's story and soon find evidence backing up his wild tale. They connect it to a kinoshimobe, a mysterious and elusive creature that violently attacks those who would defile its territory.
In the center of the kinoshimobe's territory, however, they discover something else, as well: a tree that subsists on people. Team Grimm is disturbed to discover the faces of its victims imprinted on its bark.
They determine that the kinoshimobe had been essentially feeding the tree with the bodies of those who would pollute nature. They set up a trap to lure it out, but it ends up attacking Rosalee instead. Nick kills it with an ax to the chest, and the tree consumes its body.
Since they can't exactly arrest a tree, there's nothing more for them to do.