A horror movie set during a late night show gone wrong is a concept so good you wonder why it hasn't been done already. That's the premise for Cameron and Colin Cairnes' Late Night with the Devil, a found footage/possession mystery that gained positive attention last year at SXSW before recently becoming embroiled in an AI controversy over the use of three interstitial images.

The movie itself is a twisty one that revolves around a supposedly possessed little girl called Lilly (Ingrid Torelli), the doctor who's been treating her (Laura Gordon), and troubled late night host Jack Delroy (David Dastmalchian), whose quest for ratings has made him willing to push the boundaries like he's never pushed them before.

But what exactly happens, and what are the implications behind the disturbing (and slightly mind-bending) end of the film? Let's dig in.

What's Late Night with the Devil about?

The movie revolves around the recently discovered "master tape" of an infamous Halloween broadcast of Night Owls with Jack Delroy, a fictional 1970s late night show living in the permanent shadow of Johnny Carson. Delroy's wife recently died from cancer, there have long been rumours about his involvement with a Bohemian Grove-style organisation of elites that meet out in the woods, and his second place ratings bring with them the ever-present threat of sponsorship dropout or cancellation.

The good news? Delroy has a plan to fix it all. Enter the author of Conversations with the Devil, a "para-psychologist" called Dr June Ross-Mitchell, who has been treating a little girl called Lilly. Lilly is the sole survivor of a cult that worshipped a demon known as Abraxas, and the word on the street is that she's been possessed. Delroy is hoping a late night demonstration might be the answer to his ratings issue. But things start to go wrong when Lilly seems strangely obsessed with Jack, the psychic first guest on the show Christou (Fayssal Bazzi) dies offstage, and the demonstrations grow increasingly out of control.

How does Late Night with the Devil End?

Instead of wrapping up the broadcast, Delroy decides to play back the tape of Lilly's demonstration – which saw her speaking directly to Jack as if she knew him from somewhere before levitating in her chair – to try and prove to sceptic Carmichael Haig (Ian Bliss) that it wasn't all a trick. During the playback he discovers that by slowing down the frames, he can see a haunting image of his dead wife standing directly behind him on the stage. Shortly after that, all hell breaks loose.

Lilly transforms once again into her possessed form, but this time it isn't just her face and voice that change. She levitates into the air, blurs with static like a television image, and her head splits in two while being consumed by fire. As she begins to murder the various guests and anyone who gets in her way, Delroy tries to make his escape — only to find himself trapped in a montage of different memories. In the final two he drinks from a cup while surrounded by cultists, then goes to stand beside the bed of his dying wife.

"They told you you could have it all, didn't they?" she whispers. "Be number one. Well you finally made it, darling. But you had to pay a price. Exit Millie, stage left."

His wife asks Delroy to kill her and he stabs her in the stomach, only to wake to discover he's stabbed Lilly. He's standing on stage, alone, and everyone around him is dead. We hear sirens in the background.

What really happened to Jack Delroy's wife?

From the very start of Late Night with the Devil, the idea of sacrifice lurks in the background. It's only brief, but during the stock footage we see of Delroy signing his five-year TV deal, a reporter in the background calls out, "What did you have to sacrifice to get here tonight?" The question, at least then, goes unanswered — but the real answer lies in Delroy's secretive cult-like club The Grove, described early on as "a men-only club located in the Redwoods of California". "Speculation swirls around its taste for arcane ceremony and its power to make and break careers," reads the voice-over, and this turns out to be true in the most horrifying way.

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Although it doesn't get much of a mention for a while after, Delroy's forest cult is hinted at again the first time Lilly becomes possessed. After saying, "He's here, isn't he," Lilly/the demon turns to Delroy and implies they've met before. When Delroy denies this, Lilly tells him not to be a fool.

"We go way back," she snarls. "We met amongst the tall trees."

When we start to piece these moments together, the final scene where Delroy speaks to his dying wife suddenly makes a lot more sense. The implication is that Delroy made a monkey's paw-style wish in the forest to become the number one late night host. The same demon that's taken over Lilly answered his prayers, but in return it took his wife's life. Delroy ended up getting his wish to become number one on the ratings, but he had to sacrifice everything to get there.

How to watch:Late Night with the Devilpremieres in theaters March 22, and heads to Shudder April 19.