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 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, supply drops have stopped and on the day their punishment is meant to end, the Warden does not come. Instead a sheep appears; but sheep can't swim. Aina becomes convinced that they've been abandoned, and that Whitney has been keeping secrets.

As she starts testing the limits of their prison, investigating ways she might escape, she is confronted by decisions that haunt her past. Little does she realise that her biggest choice is yet to come...