Searching through a little-used cupboard at home, TV history man Glyn Peters chances upon a photograph he has never seen. Taken in high summer, many years before, it shows his wife, Kath, holding hands with another man. Glyn's work as a historian should have inured him to unexpected findings and reversals, but he is ill-prepared for this radical shift in perception. His mind fills with questions. Who was the man? Who took the photograph? Where was it taken? When? Who else knew? Had Kath planned for him to find out all along? As Glyn begins to search for answers, he and those around him find the certainties of the past and present slipping away, and the picture of the beautiful woman they all thought they knew well distorts, changes, grows mistier.