The new episode follows film student Davis (Samuel Blenkin) who takes his girlfriend and fellow student Pia (Myha'la Herrold) to visit his hometown. When Pia learns that the town was home to a series of horrifying murders by serial killer Iain Adair who, it's thought, caused Davis's father's death, she persuades Davis to create a true crime documentary. But they uncover secrets incredibly close to home.
In one of the ultimate Black Mirror twists, Pia stumbles across a VHS tape that reveals that Davis's parents were also in on the crimes - torturing and murdering visitors to the town.
Recalling her reaction to the big twist, Herrold told RadioTimes.com and other press: “I was not expecting it at all, my jaw was on the floor, I was like ‘this is so morbid, I can’t believe what I’m reading’. And then the second time round, Charlie [Brooker]’s so clever, there’s tiny things that’ll sort of lead you into thinking, 'blah blah blah'.
- Black Mirror actor reveals unsettling double meaning in Loch Henry
- Black Mirror Loch Henry ending explained: What happened to Pia?
"Some of the signs were there if you were really looking for them, but you would have to be looking with a magnifying glass, he’s so clever about it. No, I was gagged – gooped and gagged.”
Fans have spotted some of the signs that Herrold may be referring to, including some strange turns of phrase from Janet, Davis's mother, earlier in the episode. At one point, she refers to Adair as "stupid" - a bizarre way to refer to the man who supposedly killed her husband.
Others have pointed out that Pia's death was foreshadowed earlier in the episode, when Davis tells her that the countryside can be a dangerous place and that one wrong step can kill you.
There's also the small matter of Davis's dad Kenneth having the same nickname as protagonist Kenny in season 3 episode Shut Up and Dance, which should have given viewers some clue that all was not as it seemed with him.
Meanwhile, the actors also pointed towards the BAFTA award at the end of the episode having a sinister double meaning.
Blenkin said the final scenes of the episode, during which Davis is awarded a BAFTA following the release of the documentary, are what drew him in.
He added: "Those last scenes of the episode, that’s what really drew me to the character and I thought ‘I’m so excited about filming’. For me, that is an imaginative, emotional sort of goldmine of stuff to work with and it’s hugely prescient and exciting to play.”
More like this
Take part in the Screen Test, a project from Radio Times and the Universities of Sussex and Brighton, to explore the role of television and audio in our lives.