Darkfield started out making shows in containers. At previous Fringes, you might have caught Seance at Summerhall or Flight the year after. They specialise in immersive theatre. Pre-pandemic, audience members were herded into the container. The interior was dressed as a luxurious dining room – or an aeroplane cabin. You took a set of headphones, you took a seat, you were invited to shut your eyes – and the story began.

Knot: The Trilogy sees the company experimenting with an audio experience that you can enjoy at home. Or more or less at home. And enjoy probably isn’t quite the right word either. Knot is intriguing, discombobulating, thought-provoking and thrilling. But as I sat in the car, tense, sweating slightly, sitting on my hands to avoid flinging the car door wide, enjoyment wasn’t right at the top of my list of adjectives.

Their latest offering is served up in three parts. You download the Darkfield Radio app, pop in a triplet of codes that you’re sent before the show starts and the app will send you a wee nudge before each ‘episode’ is due to begin. You’re asked to find yourself a park bench for the first instalment in the trilogy, a car for the second and retreat to your home for the third. Obviously you don’t have to go to any of these locations – you’ll still get served the story – but visiting the bench and the car (if you can lay your hands on a car) accentuate the transience of our actions and heighten the hyper-unreality.

Darkfield serve up superlative soundscapes. They make exquisite use of binaural recording to create the impression that the stray ball is bouncing right past your feet, the child chasing it has come to a standstill right in front of your bench. You hear the birds and the ambient noise in the park, the passing traffic and the rain beating on the roof of the car but the remarkable bit is when you hear the car door open behind you – and have to look round to check because someone should, by rights, be actually there.

As with their other shows, tricky to trail the story without giving anything away. The story starts with a girl sitting on a bench in a park. She can’t remember how she got there. There’s something of Sarah Kane in the lilting, lyrical but distinctly unsettling commentary. And there’s a lot of Christopher Nolan in the joyous subversion of your expectations. And the three parts of the story layer beautifully one atop the other, in a way that eventually makes a mind-boggling, disorientating sense.

Whether the sense is worth £22.50, the ticket price for the trilogy, is another question. It seems churlish to mention the ticket price because many would be perfectly willing to pay this to walk into a theatre. But whilst served up in 3 parts and so sort of lasting the billed two and a half hours, in actual fact, the first two parts are twenty minutes each and the third, twenty-five.

If you were sat at Summerhall with a friend or two and a drink or two in the gaps, you possibly wouldn’t question the cost. Sat at home, maybe you might – though the production values are superb. The app works without a glitch. The sound quality is tremendous. With such a complicated technical endeavour, you no doubt get what you pay for.

We’ve been offered an abundance of audio theatre over the past eighteen months, most of it not a patch on this. This audio theatre invades your head like a sinister jester of an ear worm and makes you question whether what you presumed was reality, is really real at all. Marvellous stuff.