Ah, the butler did it. Or maybe it was the jealous wife. Or was it all a dream…?

Thankfully we’re in an era of brilliant TV, which means we’re largely (although not completely) free of the above groan-worthy tropes.

Writing for television is a skill, though. And when it comes to thrillers in particular, there are a set of tools that guarantee we as viewers will be at the edge of our sofas watching from between our fingers.

The latest example is new four-part thriller, Cheat. With a dangerous relationship at its heart, ITV promises it will “keep audiences guessing from the start”.

That relationship is between university professor Dr Leah Dale (Mr Selfridge’s Katherine Kelly) and her student Rose Vaughan (Three Girls’ Molly Windsor).

Leah suspects Rose of cheating on an essay and is determined to prove she did it. The situation escalates horrifically, locking the two women in a deadly game of cat and mouse — or as director Louise Hopper puts it, “cat and cat”.

But how did its writer Gaby Hull pull it off?

There are a few smart, reliable techniques that screenwriters like Hull employ to keep their audience with their fingernails between their teeth and debating with friends over water coolers the next morning.

Here are the tricks of their thrill-delivering trade…

6 tricks TV writers use to keep us hooked