On Erin Island, an idyllic fishing village off the coast of Ireland, charming inebriate Ciaran O'Shea is tasked with showing police officer Lisa Nolan her new beat. But strange doings are aloof. The crew of a fishing boat disappears, whales start appearing dead on the shore, and a local lobsterman catches a mysterious tentacled creature in his trap. Soon it becomes clear to O'Shea and Nolan that there's something unnatural out there, and it's hungry....