The Teacher season 2 delivers a harrowing, yet unsurprising ending

Zac and Matt's brotherhood had faltered due to the former making a pass at Jimmy's son, resulting in considerable tension between the pair, and while Matt had feelings for Sienna, she had been seeing someone else, and was expecting a baby as a result.

Had Matt, overcome with rage, done something unforgivable and irreversible?

As for Tim, he secretly travelled to the Mallory Centre, where Zac had been killed, while pretending he was at home suffering with migraines, and Dani also uncovered scores of deleted messages between the two on her husband's phone.

Was Tim a predator who had an unhealthy obsession with teenage boys, one being Zac?

Both theories were plausible but as the drama headed into the home straight, their names were cleared as the true perpetrator was revealed – and no, it wasn't headmaster Caulfield, which would have been quite the twist indeed.

The Teacher season 2 ending explained: Who killed Matt and Sienna?

It was Matt's dad Jimmy, a colleague of Dani's with whom she'd had an affair and Tim's best friend, who was responsible for both deaths.

He had groomed Sienna, a vulnerable student who was living in care, and was also the father of her baby, a secret they'd both tried to protect. But after Zac had spotted teacher and student together in Jimmy's car a few days earlier, he told Sienna that he was going to tell Dani the truth.

When Jimmy found out that his abuse had been exposed, he instructed Sienna to "keep him quiet", which resulted in an argument between the pair and Zac's eventual death after she struck him over the head with a rock.

While Sienna technically murdered her friend, it was Jimmy's manipulation of the teenager which created the environment for her to commit the harrowing act, before she then suffered a similar fate.

A short time later, Sienna was found dead after being suffocated by Jimmy.

She had met him under the cover of darkness, where they'd argued about her pregnancy. While she wanted to keep the baby, Jimmy demanded that she have an abortion. When she refused, he silenced her permanently.

Read more:

• The Teacher's Will Mellor on "new" experience working with intimacy coordinator for sex scenes
• The Teacher star Will Mellor was "worried" about one "emotional" scene

While it's a deeply disturbing revelation, it's also entirely unsurprising.

Like BBC drama The Jetty, which explored the abuse of underage girls in a Northern lakeside town, The Teacher season 2 also highlights how the sexual exploitation of young women so often happens right under our noses, and is carried out by those who seem so ordinary, and anything but predatory.

It's only when tragedy strikes, however, that the true nature of men like Jimmy is laid bare. They disguise their dark intentions, hiding in plain sight, and the world continues to turn around them while their victims' lives stumble and stall – sometimes permanently, in the case of Sienna and Zac.

Jimmy's behaviour was monstrous, but you won't find him lurking in the shadows, sharpening his horns. He's the man sat next to you on the tube, the neighbour who offers to feed your cat while you're on holiday, your daughter's maths teacher.

Monstrous, yes – but not in the way horror stories would have have you believe.

The Teacher is available to stream on My5.

Check out more of our Drama coverage or visit our TV Guide and Streaming Guide to find out what's on. For more from the biggest stars in TV, listen to The Radio Times Podcast.