Regret resonates across the fourth episode of The Fall like the sound of a gunshot down the corridors of Belfast’s police station.

So dark is The Fall that – at the show’s halfway point – we’re now fairly certain that its creator Allan Cubitt wrote it in a mixture of kitten blood and the tears of toddlers who’d dropped their ice cream.

The Fall seems dead set on setting itself apart from other crime shows. Not because we know who the murderer is – Columbo hung its raincoat on that particular chair 44 years ago – but because it’s so desperately grim that it makes its Danish contemporaries look as light-hearted as Murder, She Wrote. It’s a show so darned dark that it forces you to adjust the brightness settings in your own mind, as well as your telly.