Over the last three years, I’ve gained a new annual tradition. In the drained days of the new year, with the Christmas lights packed away and no reason to leave the house, I go to ground with the latest instalment of Tim Pears’s West Country trilogy. His project – a layered, lyrical portrait of early-20th-century England, begun in January 2017 with The Horseman and continued in January 2018 with The Wanderers – concludes this year with The Redeemed, in which he draws the stories of his protagonists, Leo and Lottie, to something like a close. These are novels that, in their attentive, slow-building descriptions of a seasonal, rural world, attempt to reconnect us with something we’ve mostly lost: a sense of the rhythm of the natural realm and our place in it. By tying the publication of his books to a singular point on the calendar, Pears manages the neat trick of creating a physical connection between form and content; of amplifying the message of his books through the act of reading them. And with The Redeemed, that connection is intensified: the sense of homecoming that came with picking up the latest volume this month is echoed and augmented by the story between its covers. In the final book of Pears’s trilogy, his wanderers are returning.

Leo’s road, in particular, has been winding. A carter’s son with a rare affinity for horses, he was born in 1900 on an estate tucked into a Somerset valley on which the landowner’s daughter, Lottie, was growing up, too. The first volume absorbs its readers into a long-vanished landscape in which Leo – silent, watchful – exists as a kind of spirit of the place, observing every creature, every leaf, every ripple in the weather with profound attention. Only Lottie is able to rouse him: a product of her environment too, she’s nevertheless quicker, brighter, less accepting than he. The bond they form is deep, but it transgresses social hierarchies that are, in their way, as fixed and dictatorial as the seasons. Book two sees them forcibly sundered; exiled from Eden and thrown into a wider world from which, until then, they’d been sheltered. While Lottie’s journey is largely metaphorical, a voyage from innocence to experience that reveals to her the limits imposed on her as a young woman, Leo’s is literal. Ejected from his home, rejected by his family, he takes to the road, and encounters a colourful cast of fellow travellers (kindly Gypsies, brutal farmers, a philosopher-tramp, a shepherd who castrates lambs with his teeth) who open his eyes to possibilities and perils previously unimagined. By the end of the book, however, the tide of history has overtaken them. The first world war is upon Leo and Lottie, and the time for personal voyages is over.

The Redeemed begins with Leo farther from home than ever. It’s 1916, he’s as old as the century and, like nearly every able-bodied boy, he’s a tiny cog in the country’s great war machine. Rather than churning over the mud of the trenches where, given Leo’s skill with horses, he might easily have fetched up, Pears elects to send him north, to take the stage in a less mythologised theatre of war. Water swirls and swells through Pears’s trilogy, frequently taking on additional meaning, and Leo begins the final instalment literally and figuratively at sea, as a deckhand on the HMS Queen Mary on the eve of the Battle of Jutland. For a series that trades on the intimate and the natural, the battle scene represents a whiplashing change of pace, and Pears dispatches it expertly, conveying its sound and fury through Leo’s eyes, his outlook shaped by the countryside and the Bible. The sinking of the Queen Mary, in a frenzy of “fire and smoke and sulphur”, calls to mind scenes from Revelation, while in the crackle of the deck’s heat-scorched resin he hears “a noise like burning holly”. In Somerset, meanwhile, though the fighting feels distant, its reverberations are deeply felt. Lottie manages to parlay the absence of young men into a job for herself as the local vet’s assistant, a role in which she thrives until an encounter that serves as a violent reminder that not even war has eroded all the disadvantages of being born female.

While both protagonists survive their battles, they are irrevocably transformed by them. Pears follows their faltering, fumbling attempts to find a way back to each other and to themselves – a process that involves a reckoning with former ideas of what home is. The old, constant world in which the seasons unfolded with clockwork regularity and everyone knew their tasks has passed; The Redeemed looks to a future that offers new freedoms, but at great costs. “I’m a modern man, you see, Leo,” offers the farmer on whose land Leo lives towards the end of the book, explaining the tractor in his yard. Of his horses, now redundant, he says airily: “The knacker’s yard’ll take ‘em, if no one else will.” As a piece of nature writing, Pears’s West Country trilogy is exemplary, a feat of perception and description that earns him a place among a pantheon that stretches from Thomas Hardy to Flora Thompson. Its greatest achievement, however, may be in the sense of bereavement it conjures for a world gone by, and the accompanying awareness that, unless we start paying attention, we have just as much to lose in the future. For me, that sense is compounded by the realisation that my new tradition is over. What I’ll do next January I don’t know.

• The Redeemed by Tim Pears is published by Bloomsbury (RRP £16.99). To order a copy for £12.99, go to guardianbookshop.com or call 0330 333 6846. Free UK p&p over £15, online orders only. Phone orders min. p&p of £1.99.