For twelve years Aina and Whitney have been in exile on an island for a crime they committed together, tethered to a croft by pills they must take for survival every eight hours. They've kept busy - Aina with her garden, her jigsaw, her music; Whitney with his sculptures and maps - but something is not right. Shipwrecks have begun washing up, and their supply drops have stopped. And on the day they're meant to be collected for parole, the Warden does not come. Instead there's a sheep. But sheep can't swim.