I hate it when people describe television as a rollercoaster ride, but there is one sense in which Line of Duty (BBC One, Sundays 9pm) fits the description: your heart is racing before it even begins. Four seasons of this cop drama have trained the body to expect thrills. Each one has been nastier and battier than the last.
Our heroes are the anti-corruption unit AC-12, which exists to police the police. Each of them could do with a firm hand themselves. Superintendent Ted Hastings (Adrian Dunbar) has a broken marriage he can’t let go; Detective Sergeant Kate Fleming (Vicky McClure) has kids she never sees; Detective Sergeant Steve Arnott (Martin Compston) is a 4ft-tall Casanova. And whenever these pen-pushers enter a room, the temperature drops. Can you blame the other rozzers for hating AC-12? Imagine how hard your job would be if tiny Steve Arnott turned up at 5pm every day and went through your briefcase to make sure you weren’t nicking the stationery.
