Life is good for university friends Sarah, Ruth, Charlotte and Kathy - it's summer, exams are over and they're escaping to a cabin by the Blue Pool. But then Sarah disappears without a trace. Twenty-five years later, a man walks into a police station, claiming to know something about the missing girl. Suddenly, the three women – now estranged – all become suspects. For not everything was as it seemed and the greater the secret, the deeper it lies...