The High-and-Dry is a windswept land that is being fast lost to the ever-growing sea. The only things left are seagulls, seaweed, twins Luna and Oona, and their Grandad Mull. Luna and Oona have grown up listening to Grandad Mull’s stories about the dastardly shape-shifting fishfolk who live in the sea around them and cause the waves to swallow the shore with their spells. Storms sent by fishfolk are the reason why Grandad Mull is all that is left of their family, he says. But when Luna and Oona meet a fishfolk for real, Luna begins to question her grandfather's stories much to Oona’s confusion.