A visceral, emotional and high-stakes portrayal of life in a British prison; 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. However when one of the most dangerous inmates identifies his weakness, Eric faces an impossible choice; between his principles and his family. A story of guilt and forgiveness, punishment and penitence, both Eric and Mark are trapped by their pasts and unsure of their futures.