There are only 93 inhabitants on the island of Osea, off the coast of England, and if The Third Day is to be believed, every single one of them is creepy. When the main characters of this miniseries come to Osea, they encounter strange symbols, altars and rituals, along with menacing inhabitants spouting cryptic warnings. The show's six episodes are split into two halves, labeled "Summer" and "Winter," and in each part, an outsider comes to Osea and is quickly drawn into what appears to be dangerous cult activity. It’s the kind of story that will have viewers screaming "Just leave!" pretty much the entire time.

But neither Sam (Jude Law) nor Helen (Naomie Harris) leaves Osea, even when they’re potentially given the chance to do so early in their visits. Osea is connected to the mainland by a causeway built by the ancient Romans, which is only accessible for short periods of time each day when the tide is out. Viewers could make a drinking game out of how often characters talk about when the causeway is open, and it becomes almost a joke how often Sam or Helen are told they have a limited amount of time to get to the causeway, only for them to waste that time and then be stuck on the island another day.

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In "Summer," Sam comes to Osea after spotting teenager, Epona (Jessie Ross), attempting suicide near a stream on the mainland. He cuts the rope she used to hang herself and agrees to drive her home to Osea rather than taking her to a hospital. Concerned that she’s reacting to abuse at home, he insists on following along with her as she seeks refuge with the Martins (Paddy Considine and Emily Watson), a seemingly friendly couple who own the island’s only pub and inn. Mr. Martin is aggressively cordial while Mrs. Martin is a bit more confrontational, and as Sam spends more time on the island, the Martins dig deeper into his personal life, which includes a shady business deal back home and the mourning of a child who died years earlier.

In "Winter," Helen travels to Osea with her daughters Ellie (Nico Parker) and Tallulah (Charlotte Gairdner-Mihell), ostensibly as a holiday for Ellie’s birthday, but clearly with ulterior motives that she doesn’t want to reveal to the kids. They arrive to discover that the cottage they supposedly booked to stay in is suddenly unavailable, and the island seems rundown and half-deserted with abandoned construction sites and graffiti everywhere. It’s not clear if it’s been months or even longer since Sam was on the island, but Helen and her daughters eventually also cross paths with the Martins, who once again take in the outsiders and start prying into their personal business.

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In the "Summer" episodes, director Marc Munden often uses uncomfortable close-ups of the increasingly unhinged Sam, who was already dealing with mental health issues before coming to Osea. Munden fills the frame with bright, sometimes blinding light, conveying the oppressive heat and Sam’s feeling of being trapped on the island. The "Winter" episodes, directed by Philippa Lowthorpe, have a more subdued visual style, but Lowthorpe still stays close on Helen, who is more clear-headed than Sam but still makes plenty of dumb horror-movie decisions. "Why didn’t we leave?" Tallulah asks her mother at the end of their first day in town, and it’s hard not to keep asking those questions throughout the series.

Of course, Sam’s and Helen’s pasts are inextricably tied to the island, as they learn over the course of their time there, and this is the kind of place where you can check out any time you like, but you can never leave. Considine and Watson are effectively unsettling as the ingratiating but sinister Martins, who at first appear to be allies but are always pursuing their own insidious agendas. Katherine Waterston plays an even more deceptive character: an American academic studying the island’s traditions who seems like a rational, impartial observer at first, until Sam and Helen each learn more about her.

There are strong echoes of 1973 cult classic The Wicker Man, as well as Ari Aster’s Midsommar (2019), the films of Ben Wheatley (2011’s Kill List, 2013’s A Field in England) and the overall tradition of British folk horror, especially in the "Summer" episodes. But spreading these two stories, which hinge on the main character discovering one big secret, over three hour-long episodes each becomes tedious and repetitive, especially in the "Winter" episodes, when viewers already know so much about the island’s horrors. Every episode features multiple scenes of Sam or Helen merely wandering around the island, lost and confused, and the material could have been condensed to one episode (or maybe a feature-length installment) each, with the same overall effect.

The Third Day was co-created by veteran TV writer Dennis Kelly and immersive theater impresario Felix Barrett, the mastermind behind interactive live experiences like Sleep No More, and the show sometimes feels more like a world-building exercise than an engaging narrative. There is even a live element to it, with a broadcast titled "Autumn" set to air online (for U.S. viewers) and on British TV on October 3, a one-time show meant to fill in some gaps between the two halves of the season.

But the problem with The Third Day isn’t that it has narrative gaps. The problem is that the atmosphere far outweighs the narrative, that it very slowly builds to revelations that just aren’t very interesting. Sam and Helen traverse the island over and over again with growing distress, but viewers who are able to leave Osea probably won’t want to stick around.

Starring Jude Law, Naomie Harris, Katherine Waterston, Nico Parker, Charlotte Gairdner-Mihell, Paddy Considine and Emily Watson, The Third Day premieres Monday, Sept. 14 at 9 p.m. ET/PT on HBO.

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