There’s a particular kind of dread that only isolated islands can produce, and Riley Sager has built a career out of mining it. In “The Unknown,” the bestselling author of “The Only One Left” and “Final Girls” sends a film crew to a fog-bound speck of land off the Vermont coast, chasing a hundred-year-old mystery that swallowed a group of spiritual mediums whole. Nobody who set out to explain their disappearance back then ever fully did, and Sager wastes no time suggesting that whatever took them hasn’t gone anywhere.
The setup is vintage Sager: a small, closed cast; a location that might as well be its own character; and a present-day narrator whose professional curiosity curdles into something more personal the longer she stays. The research trip that opens the novel is meant to be routine, fodder for a documentary, but the island resists being filmed, catalogued, or explained. Old journals surface with pages missing. Locals answer questions with more questions. And the further the crew digs into what happened to the mediums, the more their own presence starts to feel like a repetition of history rather than an investigation of it.
What Sager does best here is atmosphere, and “The Unknown” leans hard into his strengths. The prose is spare and propulsive, built for readers who want to finish a chapter and immediately start the next one, but he still finds room for genuine unease: fog that never quite lifts, a coastline that seems to rearrange itself, the sense that the island is keeping time on its own terms. The dual timeline, past mediums and present-day film crew, is handled with more discipline than some of his earlier books, each thread earning its cliffhangers instead of just borrowing tension from the other. Readers who came to Sager through “Home Before Dark” or “The House Across the Lake” will recognize the machinery, but it’s tuned tighter this time.
Critical response has largely tracked with Sager’s usual reception: strong praise for pacing and setting, with reviewers noting that the book’s back half resolves its mysteries a touch more neatly than its slow-burn first two-thirds might suggest. Several critics have singled out the historical mediums’ storyline as the more haunting of the two, wishing it had been given even more room to breathe, while others have praised Sager for finally giving his present-day protagonists interior lives that don’t feel purely functional to the plot. The consensus, more or less, is that this is Sager operating near the top of his game, even if it doesn’t fully reinvent his formula.
It doesn’t need to. “The Unknown” delivers exactly what its cover promises: a fog-soaked, slow-creeping mystery that trusts its readers to sit in discomfort before handing them answers. It’s an easy recommendation for anyone who likes their thrillers with a little salt air and a lot of secrets, and a satisfying entry point for readers who haven’t tried Sager yet. Just don’t expect to want the lights off when you finish it.
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