Every autumn, John Pentecost returns to the Lancashire farm where he grew up to help gather the sheep from the moors. Generally, very little changes in the Briardale Valley, but this year things are different. His grandfather - known to everyone as the Gaffer - has died and John's new wife, Katherine, is accompanying him for the first time.Every year, the Gaffer would redraw the boundary lines of the village, with pen and paper but also through the remembrance of folk tales, family stories and timeless communal rituals which keep the sheep safe from the Devil. This year, though, the determination of some members of the community to defend those boundary lines has strengthened, and John and Katherine must decide where their loyalties lie, and whether they are prepared to make the sacrifices necessary to join the tribe..