One day, whilst searching in a cupboard, Glyn finds a sealed envelope with the words ‘Don’t Open – Destroy’ scrawled on it by his wife, Kath. Compelled by curiosity to ignore her instruction, he breaks the seal to find a photograph showing Kath holding hands with another man. Suddenly this one act of betrayal – hidden, concealed for many years – obsesses Glyn as he tries to get to the root of Kath’s infidelity. But what other lives will be torn apart as he recklessly delves into the past, and what is the truth about Kath?