Twitter seems like the kind of place a novelist like David Mitchell would feel at home; it’s a platform that allows for shifting identities, where new accounts appear in unexpected contexts, only to slip away and return with a different name and face. Mitchell has a proven fondness for interpenetrating planes of narrative, crosshatchings of history, fiction, and speculation that hint at deeper truth, and Twitter lets you experiment with these simultaneities, or at least watch them play themselves out.

It’s not surprising, then, that Mitchell’s newest novel, Slade House, began life as a series of tweets. In April of 2014, Mitchell created @david_mitchell, a new personal account, in order to spin the 280-tweet short story, “The Right Sort.” In the story, a teenage boy named Nathan Bland accompanies his mother to a mysterious house in Slade Alley, the home of Lady Briggs, and has a frightening hallucination that he attributes to a valium he stole before the outing. Although Mitchell’s British publisher said the author was not planning to have a new book for a few years, “The Right Sort” waylaid him: “Accustomed to having his next few novels thoroughly mapped out, David Mitchell was not expecting to be ambushed by this one, but it proved irresistible,” a spokesperson for the publisher told the Guardian last year. The 280-tweet story, with some tweaks, became the opening of a slim 238-page book.

A few surnames have shifted—Lady Briggs is now Lady Grayer and narrator Nathan Bland has morphed into Nathan Bishop—and so has the narrator’s voice. On Twitter, Nathan sounded a little like Jason Taylor, the 13-year-old protagonist of Mitchell’s 2006 book Black Swan Green: astute, disaffected, and painfully aware of other people’s opinions. Perhaps the author, who has always pinballed from narrator to narrator, didn’t want to repeat himself—the Nathan of Slade House now seems to be on the autism spectrum, a perspective that Mitchell, whose son is autistic, handles deftly. But the minimal plot of “The Right Sort” is preserved, though the novel takes a much darker turn after the point where the Twitter story leaves off. And at the center of both works—as well as the next four parts of the novel, which leave Nathan and his mother to follow four other narrators—are Slade House and its supernatural inhabitants, who turn out to feed on human souls.

The eponymous haunted house is itself a masterpiece of fantasy architecture, a mansion and grounds cupped inside a city block technically too small to contain them. The house can only be reached through a small iron door in the unnervingly narrow and grim Slade Alley, but once you’re through the wall, the cramped space unfurls into a charming garden and an elegant manor. It’s a fairly common fantasy trope—one part Tamson House from Charles de Lint’s Moonheart, another part Room of Requirement from Harry Potter, with a little menacing from the Mark Z. Danielewski’s cryptic House of Leaves thrown in. But in Slade House it nonetheless feels fresh, like seeing the theme from a recurring dream reinterpreted in someone else’s work of art.

Mitchell’s books often employ massive jumps in time, space, and genre. His 2004 magnum opus Cloud Atlas, for instance, leapfrogs from 1850 to the near past, then to the present day and the far future, beginning as historical fiction and becoming thriller and farce before moving into dystopian and finally post-apocalyptic sci-fi. By contrast, Slade House is relatively sedate; its five sections occur a modest and regular nine years apart, and the action barely leaves the mansion’s grounds. The house exerts a powerful gravitational pull on both the characters and the narrative. This is partly because of the demands of the story: Slade House is the permanent home of two immortals, whose bodies are trapped in a pocket of timelessness within the house, and other characters are drawn to it precisely like flies into a web. But I suspect it’s also because Slade House, the building, has many of the best qualities of a Mitchell novel—it is beautiful, protean, labyrinthine, impenetrable to many, and never fully explained—whereas Slade House, the book, just doesn’t quite measure up.