At a seaside caravan park, sisters Isabel and Meg build sandcastles and explore the pier with the children. Unfortunately, the peaceful holiday is shaken up when their half-sister Mildred returns to a nearby cottage where her husband Paul was jailed for attempted murder of his ex-wife.

Now, with Paul newly released, the women fear he may be seeking revenge for his betrayal. When Meg takes a mysterious new lover, tensions rise. Whose footsteps are those outside? As family secrets emerge, the sisters wonder – is Paul really after them, or are their nerves getting the better of them?