In seventh-century Ireland, a scholar and priest called Artt has a dream telling him to leave the sinful world behind. Taking two monks, young Trian and old Cormac, he rows down the river Shannon in search of an isolated spot on which to found a monastery. Drifting out into the Atlantic, the three men find an impossibly steep, bare island inhabited by tens of thousands of birds, and claim it for God. In such a place, what will survival mean?