“Umbrella” is his arrival point. Starting in Edwardian England and spanning a century during which mental-health care evolved from physical barbarity to chemical barbarity, the book, which was a finalist for last year’s Man Booker Prize, is a savage and deeply humane novel. It tells the story of Audrey Death, a woman diagnosed with encephalitis lethargica who spends nearly 50 years in the hospital in a state of increasing isolation from the world. As London is ravaged by war and time, and then a new kind of capitalism, Audrey remains locked inside herself without a key. Until a doctor named Dr. Zack Busner enters her hospital and regards her as a human being and treats her and fellow patients, as Oliver Sacks did, with doses of L-dopa and, like Sacks’s patients, they wake up.

If this were a realistic novel, “Umbrella” would blow away on gusts of sentiment and outrage. But the reigning question of this novel is not, why did Audrey suffer so long, but did Busner do the right thing? It’s a challenging question, and Self has built a book to stand its echoes.

For the first time in his career, Self has put as much energy into the scaffolding of a novel as he has the sentences. “Umbrella” is an old-fashioned modernist tale with retrofitted ambitions to boot. It moves, “Orlando’’-like, between multiple points of view — Audrey, her two brothers, one of whom, Stanley, goes off to war — and three periods of time, 1918, 1971 (when Audrey is awoken), and 2010, when Busner is looking back on his life. There are no chapters and very few paragraph breaks.

“Umbrella’’ is not an easy, light read, but then again, it’s not meant to be. As a reader, it can feel slightly disorienting to be without so many of the usual corners and boundaries of fiction. But it’s also exhilarating, especially when you realise Self has ripped them out so that he can meditate on what is inside us, what is outside us, and how hard it can be to know the difference.

Self draws us to this point by setting up a series of harmonic themes he revisits in each life throughout the book. The hospitals hallways are mirrored by London’s streets, which are as enclosed as trenches of World War I; Audrey comes from a family suffused with memories of the past, and then finds herself entrapped within her own, just as Busner struggles with his conscience later; and everyone across the book speaks, moves, and thinks to a kind of metronomic rhythm that cannot help but make us think of the passage of time and self-consciousness.

“[T]he me-voice,” Busner thinks, “the voice about me, in me, that’s me-ier than me . . . so real, ab-so-lute-ly, that might not self-consciousness itself be only a withering away of full-blown psychosis.”

Self has always been a fabulous writer. There is not a novelist in England who has masticated the Oxford English Dictionary so thoroughly and fed it to his books with such ferocity. As a modernist novel, though, “Umbrella,” cannot proceed with the too-rich quality of Self’s full lexicography. It needs to have a symphonic feel to keep going, and so Self has, to a small degree, restricted his language and reduced the suppurating imagery that gives so much of his work the feel of a horrific body politic.

The result is page after page of gorgeously musical prose. Self’s sentences bounce and weave, and like poetry, they refract. The result is mesmerizing. As readers we are both inside and outside characters’ heads at once, a staggering thing when we are, as in one section, inside a doctor looking at a patient who is in turn looking within herself. The porous membrane between outside and inside is later exploited when Self shows us Stanley as a soldier, in the first battles to be fought with airplane-mounted machine guns.