He hikes through sun-dappled woods, cues up “Dog Days Are Over” by Florence + the Machine, sits down next to a waterfall, sobs operatically for a while, then gently places a child-sized striped T-shirt in the bubbling river and watches it float away. On the way back to his car, he stumbles upon a teenage girl and a younger boy, arriving just in time to see her hang herself from a tree branch and her companion run off into the forest. He saves the girl’s life and drives her home, to Osea Island, whose eccentric residents are preparing for a festival. If you’ve seen The Wicker Man, you can probably guess that things only get weirder once they arrive.

Yet for all its familiarity, The Third Day, an eerily beautiful psychological thriller co-produced by HBO and Sky UK that will premiere Sept. 14 on HBO, rarely comes across as derivative. Creators Felix Barrett (who founded Punchdrunk, the immersive theater company best known for their long-running Macbeth riff Sleep No More) and Dennis Kelly (who created the cult-hit British thriller Utopia) seem keenly aware of the mysterious-island trope. More than a pastiche, their story accesses layers of emotional resonance in centuries’ worth of lore, encompassing The Tempest and The Island of Doctor Moreau as well as more contemporary tales like Lost and Shutter Island.

Law, a classically handsome movie star who’s been one of the most fascinating actors alive since coming to TV for the title role in Paolo Sorrentino’s deeply bizarre HBO drama The Young Pope, is the perfect choice to play a character that contains multitudes. The protagonist of the first half of the six-episode series, subtitled “Summer,” Law’s Sam finds himself stuck on Osea, a real island off the coast of England whose causeway is submerged at high tide. The couple that operates the local pub (a creepily folksy Paddy Considine and his prickly wife, played by Emily Watson—a veteran of Lars von Trier’s mysterious-island masterpiece Breaking the Waves) insists he stay overnight, but Sam discovers the room he’s been assigned is already occupied by a woman (the always-great, perennially under-appreciated Katherine Waterston). Reality, dreams, substance-induced delirium and possible psychosis start to blur together. The third day of this adventure—as chronicled in an episode for which Law’s disoriented, often solo and silent performance, deserves an Emmy nomination—truly is a doozy.

To say much more about the plot would detract from the sense of confusion the show creates—one grounded enough in the characters’ consciousnesses to build suspense rather than cause frustration. “Summer” director Marc Munden (another Utopia alum and a British TV stalwart) renders Sam’s journey in startlingly bright, overexposed color, fixating on details that mingle natural beauty with death and decay: a metallic-orange dragonfly whose exoskeleton bursts to reveal swarming ants; a cute rodent with its gut slit open, surrounded by its own slick, neatly extracted, ruby-red organs. Filmed from above, luxuriant shots of the winding causeway flooded with pale turquoise water are like National Geographic photos.

The second half of the miniseries, “Winter,” is also set amid the inscrutable community on Osea. Along with a new main cast, led by Moonlight Academy Award nominee Naomie Harris, this story has a different director, Philippa Lowthorpe (The Crown, Call the Midwife)—although the frosty, gray seasonal backdrop might deserve more blame than the cast and crew for its initial tedium. In any case, the action picks up toward the end of the first hour. My take on “Winter” may also be lacking some crucial narrative context; its airing will be preceded by “Fall,” billed as a “live theatrical event” broadcast on the Internet that will follow Law and his cast mates through a day on the island in real time. This, ostensibly, is where Barrett’s expertise comes in.

Much of the project’s success is riding on “Fall”—in terms of its artistic execution as well as the number of viewers it attracts, and for how long. (Then again, has there ever been a better year to catch millions of us at home all day in search of entertainment? I’ll certainly be watching, and especially with theaters closed, fans of live performance are sure to be intrigued.) And after five episodes I’m worried the show’s finale, which wasn’t sent to critics, won’t have room to adequately resolve its most ambitious themes: grief, parenthood, spirituality, the darkness lying dormant within the human soul. A Lost-level disappointment seems at least as likely as a bonkers Wicker Man show-stopper. Still, on the strength of “Summer” and in anticipation of the experiment in hybrid storytelling that is “Fall,” The Third Day more than earns the benefit of the doubt.