When Hetty's Dad agrees that they can live in her grandparents' beach hut at Hengistbury Head, near Christchurch for the summer, she is so excited. The prospect of a fun-filled summer spent exploring and having fun takes an unexpected turn as Hetty and her new friend Charlie desperately try to evade the attentions of a strange man who seems to be watching their every move. Who is he and what does he want?