The year 1973 wasn’t an uneventful one in Britain. The country entered the European Economic Community, the lights went out and candles made a comeback during the Three-Day Week, and David Bowie killed off Ziggy Stardust. You would expect an ordinary sort of novel about the year to make a lot out of these and other headline-grabbing events. John Cromer, the narrator of Caret, prides himself, however, on not reading the newspapers. His eyes are trained, instead, on the most intimately local occurrences – on what most of us would miss, lacking the same microscopic attention to what takes place under our noses.

This is the third of Adam Mars-Jones’s novels about John. In Pilcrow (2008), we met a boisterous infant knocked down but not out by a diagnosis of Still’s disease, a rheumatic condition that inhibits his growth and leaves him largely wheelchair-confined. Cedilla (2011) took him on a journey of spiritual discovery in India and then to Cambridge University, which he found less enlightening and a little oversold. In Caret, John is transitioning into adult life, not by tearing into the world of employment (he’s considered physically barred from that), but by moving into custom-built rooms provided by Cambridge Council. Although his options are severely pared back, John seems more than satisfied – he isn’t at all a weepy character – with the treasures that everyday life reveals. There’s plenty to marvel at, even in such an apparently shrunken existence.

Like the previous instalments in the sequence, Caret is a very thick book. But it isn’t loaded with actions or developments of a standard novelistic kind. It’s a vast compendium, rather, of uncannily acute acts of observation. In John’s universe, the precise charms of a packet of Toffo sweets are more deserving of scrutiny than, say, the disputes between the trade unions and the Heath government. ‘I liked the way the folded-over wrapping left lines on the surface of the toffee,’ he tells us, ‘proof that its current tooth-resisting texture was no more than an interval between two episodes of melting, one in the factory and one in the subtle furnace of the mouth.’ The ‘glassy cerulean honeycomb’ of a geode he spots on a market stall transports him into synaesthetic raptures: for him, the rock is ‘a gorgeously calcified Friday’. When he encounters a case study, in a century-old sexology textbook, of a woman with an erotic attachment to crystalware, he feels nothing could be more reasonable. It’s a bit dull, he suggests, to restrict ‘the instinct to worship and give thanks’ to brute reproductive ends.

This isn’t to say that John is blithely materialistic or that he doesn’t care for people. As a convert to Hinduism (specifically a version espoused by the early 20th-century guru Ramana Maharshi), he regards ostensible reality as maya, or an illusion. The world is no less dazzling, however, for being ‘a series of … Potemkin villages’. He presses his new neighbour, Mark, for exhaustive details about his work as a milkman, which he considers to have a ‘riveting nullity’ that mirrors ‘the emptiness of Maya’. Events needn’t be conventionally exciting to enthral him. Caret is filled with relatively inconsequential episodes – a mouse getting stuck in a toaster, John’s misfiring attempts at finding sexual fun in public lavatories – that come bathed in a glow of the miraculous, the more so for unfolding at an elaborately leisurely pace.

It may all amount, as John admits with appealing humility, to an ‘avalanche of trivial rubble’, but the rubble lands with unusual meticulousness. You can’t fail to look up from Caret at the mass of other printed words around – in those hated daily papers, for instance – and be struck by how sloppy and generalised everything else seems by comparison. And yet John’s exactitude can be as testing for the reader as it sometimes is for his friends and carers. This is particularly the case when he returns home for Christmas dinner and the novel unhurriedly enters its climactic scene. As his unsparing eyes rove across the Cromer family home, finding nothing there unfascinating (a loose-leaf binder, a Kenwood Chef food mixer), we feel we could be in for one of those Christmases that go on forever.

John himself admits to a fondness for putting on a performance. At university, he spent three years trying ‘to show … that I was clever, funny, original and above all interesting’. He’s all of those things, but nobody can be all of them all the time. Over such a large number of pages, John’s voice comes to feel too unvaryingly bright, his preoccupations too consistently fine-grained. ‘The other day I got confused between the ichneumon fly and the dytiscus larva’ is as close as he gets to having an off moment. Caret stays very tidily within the parameters that Mars-Jones established two long volumes ago. He never surprises us with anything that diverges from the pattern of infallibly elegant zeroings-in: a howl of rage, perhaps, or an escape into the vulgar dramas raging in the wider world.

I was left thinking that Adam Mars-Jones is possibly the best prose stylist currently writing in English. His extraordinary vividness encourages us, even admonishes us, to look around ourselves with more curiosity, more sensitivity. All the same, I kept wanting him to rough up his impeccable phrasing, say to hell with punctiliousness and crack through to those levels of character – or of the illusion we call reality – that don’t necessarily call for the most sparkling sentences.