A visceral, emotional and high-stakes portrayal of life in a British prison where Mark Cobden (Sean Bean) is consumed by guilt after accidentally killing an innocent man. Accepting his four year sentence and separated from his family, he meets Eric McNally (Stephen Graham), a caring prison officer doing his best to protect those in his charge. When one of the most dangerous inmates identifies his weakness, Eric suddenly faces a tormenting choice; his principles or his family. A story of guilt and forgiveness, punishment and penitence, where Eric and Mark both are trapped by the past and unsure of the future.