In seventh-century Ireland, a scholar and priest named 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 a spot on which to found a monastery. Drifting out into the Atlantic, the three men find a bare rock inhabited by tens of thousands of birds, and claim it for God. In this novel by the author of Room, what will survival mean? And can their faith endure?