There is something not quite right about the sea off the remote Cornish town of Mythirvin. Strange midnight rituals, enigmatic neighbours and the feeling that the water is somehow watching, make recent arrivals Dylan and Mac even more convinced that the decision to move to the town was a huge mistake. Unable to resist the pull of the ocean, Dylan begins suffering odd dizzy spells that fill him with an urge to swim. Lost in the waves, he discovers the truth about Mythirvin and the extraordinary creatures that live in the sea and caves around the coast. A mesmerising world neither Dylan nor Mac could have imagined is revealed to them, but the darkness at its core and an ancient struggle between sea and land mean that the boys are dragged into a conflict they never knew existed, and cannot escape.