Jon McGregor has a quietly and brilliantly transformative way of mixing up genres. His 2017 novel Reservoir 13, winner of the Costa novel award and shortlisted for the Goldsmiths prize, began with news that a girl was missing. Search parties gathered; torchlight scoured a northern village. Even the title, with its sinister coolness, suggested that this book would follow the contours of a crime novel, and accordingly it was wise to be on the alert, paying heightened attention to each location, person and event. Gradually it became clear that we were not really there to solve the crime. All the watching and searching was failing to bring back Rebecca, but it was not without purpose. Each page, charged with intensity borrowed from the crime plot, was revealing the complex life of the village – its landscape and wildlife as well as human inhabitants – through the cycle of seasons and passing of years.

Lean Fall Stand moves into different territory entirely, but again McGregor pivots from one kind of story to another with profound effect. This new novel looks as though it’s going to be about an Antarctic expedition. It will doubtless be concerned with character and endurance under extreme pressure; struggling figures will cross the wilderness; sublimity and quotidian banter will tell upon each other. Partly that’s right; a storm strikes in the first pages and the ensuing battle for survival is narrated with riveting immediacy. But the second and third sections of this three-part book unfold far from the ice floes. Conditions remain challenging, endurance and discipline are required more than ever, but the work in hand is now the gruelling task of living with a brain injury and (for others on this most testing expedition) the task of caring for a man who has lost his powers of speech.

Robert Wright has been working in Antarctica for 30 years. He is more at home at his field station than in the family house, outside Cambridge, from which he has been so regularly absent. This season he is acting as guide and technical assistant for two young mapping specialists, Thomas and Luke. The three-way dynamics are vividly established in agile prose that slips between their different voices and ways of seeing. Robert’s talk of “radio discipline” and “correct operating procedure” meets Luke’s chilled “thanks for sharing”. In the storm, however, they can hear only snatches of each other’s voices on their radios, odd syllables adrift on white noise. Another kind of linguistic puzzle takes over in a long and extraordinary passage that records something close to Robert’s stream of consciousness as his thinking gets more confused in the unfolding disaster. “Wide noise like apple oars. Apple sauce. Appley saws. Appley laws.” He cannot reach the word applause. Tongue-twisters, nursery rhymes and riddles come to mind – but what is happening is no game. “It was sure where he’d fallen. Sore. He was sure. Shore lips.”

It is Robert’s wife, Anna, who subsequently becomes the central figure. We watch her, and watch with her, as she grasps what his physical disability and severe aphasia will mean for them both. McGregor presents a powerful portrait of a woman confronting tragic change, and of fiercely independent spouses thrown together inescapably as carer and cared-for. None of it is written as tragedy – no agonised laments, not even tears – but every line has weight. “I don’t want to be a carer,” Anna says plainly. “I never even really wanted to be a wife.” Now choice doesn’t come into it. “She had to get down on her knees to put the socks on his feet, and his feet into the trousers … She had to leave him in the armchair while she went down to the kitchen, and she had to make him promise not to move.” Fitted out with grab-rails, her remote house “feels like a passenger ferry”, and it’s going to be a lonely crossing.

How did these stories of remote expedition and domestic care come to live together in a book? In 2004 McGregor joined an expedition to Antarctica. His job was to write about the experience, and he found he couldn’t. Which is not surprising: the inadequacy of language has long been as much a theme of polar literature as the midnight sun. Successive travellers have filled notebooks with similes for the shapes of icebergs and felt descriptive strategies falling short. The White Continent has left many authors with blank pages. McGregor set the problem aside and wrote three searching, pitch-perfect, superbly crafted novels about other things, but eventually he returned. The long gestation, the retrospective look, allowed him to set his Antarctic material in relation to bodies of thought about illness, care and commitment. His difficulty with language became the stimulus for an extended investigation of what happens when words go missing in many contexts and for many reasons.

When Anna is hit by the crisis of her husband’s condition, few people in her life say anything helpful, or even appropriate. She’s an academic oceanographer; her colleagues keep wanting to “bring her up to speed” with research for a conference. Her grown-up children, superbly drawn in all their self-absorption and vulnerability, duck out of the hospital as soon as they can (“it’s a work thing”). She longs for the silence of the Friends meeting house, and the peace of her garden. As for Robert, he has just a few words on repeat. “Yes, yes, well obviously of course”. “Christ!” He can say “yes”, but he cannot reach “no”. He waves unattached syllables like flags in a wilderness, and listeners must become code-breakers, straining to understand.

Aphasia takes Robert and Anna to terra incognita they never wanted to explore. Only a few skilled speech therapists can help with mapping the terrain. Robert reaches for words that are always just beyond him, “left outside, snowed under, needing to be dug out”. McGregor is too good a writer to push the analogy. He lets the different kinds of courage, knowledge and loss sit quietly side by side.

There’s a dreadful and delicate poetry in Robert’s struggle for articulation. When he’s tapped on the shoulder: “Soul. Soul. Soul. Jar. Soul, jar … Well. Soldier, soldier.” You might think you were in a Gertrude Stein novel, or James Joyce’s Finnegans Wake, and for good reason. Many modernist writers were deeply interested in language loss, the creative rhymes and substitutions that patients employ, and what they might reveal about our processes of communication. Samuel Beckett was preoccupied all his life with failures of articulation. George Steiner noted that in some cases the results of aphasia, rich in neologism and metaphor, “are almost inspired”. “There is a sense in which a great poet or punster is a human being able to induce or select” from fluent aphasia, he ventures, proposing the “Sinbad the Sailor” passage in Ulysses as an example.

Yet Lean Fall Stand is unusual in the patience and precision of its engagement with a particular clinical disorder. The task of rendering dysfluent thought and speech must have been formidable. McGregor transliterates slurrings, half-words, and phonetic misfires, repeating the same few phrases while keeping emotion and atmosphere mobile. When Robert reluctantly attends group therapy sessions, his voice and silences are heard next to other people’s disordered speech – for example that of Peter, a fluent aphasic whose sentences swell in rhythmic tides without conveying what he wants to say. “Certainly we were all dreaming of the water from here to there and the you to him to her that came upon the water wished and well we wish you well.” We might pause over the gravity, beauty and imaginative possibility here, holding that aesthetic response in precarious relation to the aphasic’s pain and frustration in not being understood.

Group therapy is an intriguing choice of subject matter. As participants are urged to choose smiley or unhappy emojis to describe their week, and dancers arrive to encourage expression through movement, the whole narrative feels poised between scepticism, impatience and admiration. Robert walks out twice. But the novel holds us there in the room. It’s in these sessions that we come closest to the kind of collective voice that McGregor has explored in previous novels – in the shared narration of the troubled, vociferous, unheard addicts of Even the Dogs, rising between them like a Greek chorus, and in the passive, impersonal recording of the whole village in Reservoir 13. Now the strenuously made words of the group members float together on a common stream of effort.

Lean Fall Stand doesn’t have the lyric force and structural patterning that gave Reservoir 13 such extraordinary rhythmic momentum. Nonetheless, it’s a novel of complex feeling and beautiful restraint from one of the finest writers around.

• Alexandra Harris’s Weatherland: Writers and Artists Under English Skies is published by Thames & Hudson. Lean Fall Stand by Jon McGregor is published by 4th Estate (£14.99). To order a copy go to guardianbookshop.com. Delivery charges may apply.