Like Richard Hannay, I had to run to catch the early morning train from London to Edinburgh. Thankfully, unlike Hannay, I wasn’t wanted for murder — I’d merely overslept again. As the train pulled out of King’s Cross, I fished out my old Penguin edition of The Thirty-Nine Steps, Hannay’s first — and most famous —adventure. Each time I reread it, I marvel at what a brilliant book it is — how modern it still seems, how easily it draws you in. As we raced through England towards Buchan’s beloved Borders, I rejoined Hannay on his mad dash across the country, urging him on in his heroic quest to save Britain from the beastly Hun. By the time I’d turned the final page, we’d already reached Berwick. Buchan understood the value of clear and simple writing. He also knew the power of a rattling good yarn.

This year marks the centenary of the publication of The Thirty-Nine Steps — the template for countless spy stories and the inspiration for Hitchcock’s greatest film. A hundred years since Buchan wrote this slim book to wile away a dreary convalescence, his hero Richard Hannay remains the archetypal man of action, the father of James Bond. The Thirty-Nine Steps is a tale of derring-do, but it’s also a heartfelt homage to the landscape of the Scottish Lowlands. What better way would there be to mark this centenary than to visit Buchan’s native land, guided by his granddaughter, Deborah Stewartby? It feels a bit like playing truant, but isn’t that what The Thirty-Nine Steps is all about?

Lady Stewartby meets me off the train at Waverley, demurely dressed in pale green tweed, as elegant and timeless as one of Buchan’s heroines. For her, Buchan’s legacy has been nothing but a bonus — she’s full of admiration for him — but for her father, William Buchan 3rd Baron Tweedsmuir, the writer’s fame cast a longer shadow. The second generation of descendants is always freer than the first.

We drive through Edinburgh, past the Pentland Hills and out into rolling countryside. Now we’re in the Borders, a land unknown to most Englishmen. I’ve only been here once before and had forgotten how beautiful it is. It’s gentler than the Highlands, a pattern of rounded hills and soft meadows. ‘Such an important part of what he writes about is the landscape,’ says Deborah. You can see why he set so many stories here. It’s a perfect hideaway.

Buchan was born in Perth, brought up in Glasgow and spent much of his adult life in England, but here in Tweeddale is where his soul resides. This winding river valley was his mother’s homeland. This was where he spent his youthful summers, hiking across the moors and fishing in the Tweed. ‘Borderlands are special,’ says Deborah. Her grandfather agreed. ‘My chief passion,’ he recalled, ‘was for the Border countryside, and my object in all my prentice writings was to reproduce its delicate charm.’ His thrillers were really pastorals. As Graham Greene observed: ‘What is remarkable about these adventure stories is the completeness of the world they describe.’

It’s tempting to treat Buchan’s books as treasure hunts, but it doesn’t really work that way. ‘John Buchan was a novelist,’ says Deborah. ‘He wasn’t writing a guidebook.’ There are some local landmarks in his novels but that’s not what Buchan is about. His great achievement lies in capturing the subtle ambience of the Lowlands rather than shackling his stories to specific sites. He conjures up the atmosphere, the feeling of a place. ‘The air had the queer rooty smell of bogs, but it was as fresh as mid-ocean,’ says Hannay. ‘It had the strangest effect on my spirits. I actually felt light-hearted.’ Breathing in this fertile scent of wood and water I realise what he meant.

We arrive in Peebles, a handsome market town surrounded by a ring of bare-backed hills. The setting is spectacular, an inspiration for any writer. Buchan’s family owned Bank House, a robust townhouse beside the Tweed, but the main attraction is the John Buchan Story, a charming museum in a grand old hunting lodge on the high street. There’s loads of personal ephemera — photos, letters, bric-a-brac — which really bring him back to life. ‘He’s much loved in this part of the world,’ says Deborah, and the museum articulates that affection. Buchan loved the Borders and the Borders still loves him back.

Deborah shows me round. She’s far too modest to admit it, but she’s played a large part in the museum’s success. A couple of years ago, it was even visited by the Queen. A reading room contains a complete collection of Buchan’s published works, together with letters from luminaries such as Rudyard Kipling, Winston Churchill and Lawrence of Arabia. ‘I cannot thank you enough for all the help you gave me with my speeches,’ reads a letter from King George VI.

Born in 1875, the son of a Presbyterian minister, Buchan squeezed the work of several lifetimes into 64 crowded years. A lawyer, a politician and a journalist (for TheSpectator), he ended up a baron and Governor General of Canada. He died of a brain haemorrhage in 1940, in Montreal.

Deborah never knew her grandfather (he died before she was born) but her father told her a lot about him. The portrait she paints for me is of a kind and courteous man — a natural diplomat, but (like many great writers) reticent and withdrawn. ‘There was always a part of him that he kept to himself,’ she says. ‘He was a very private man.’ Although he was talented in so many ways, the success of The Thirty-Nine Steps astounded him. ‘He never got over his amazement at how popular it was.’

Buchan wrote four more Hannay novels (‘he was a practical Scot, and he discovered that they made money’), but though they were mainly written for fun and profit, Deborah believes these books also had a higher purpose. ‘JB had two things that he wanted to say — always. One was that the veneer of civilisation is very thin… And the other thing was, he wanted people to realise that evil comes in very attractive forms.’ It was an important message for those difficult times — and for our times, too. ‘I think people are discovering that he had things to say about much that is troubling us now.’ Hannay’s second adventure, Greenmantle, about a charismatic guerrilla leader who whips up an Islamist uprising in the Middle East, could almost have been written with Osama bin Laden in mind. Yet Buchan never forgot that writing is useless unless it entertains. ‘A story has to have a beginning, a middle and an end, and he was a very good storyteller,’ says Deborah.

Despite a succession of demanding jobs and a lifetime of ill-health (probably Crohn’s disease, still undiagnosed at the time) Buchan somehow managed to write 100 books. ‘The thing I wish I had was his powers of concentration!’ says Deborah. His 30 novels are best remembered, but he also published numerous biographies, and a 24-volume history of the Great War, written contemporaneously, which appeared fortnightly in the Times.

His life was far from plain sailing — his brother and his best friend were killed on the same day in the first world war — but his Calvinist upbringing gave him an inner resilience and self-discipline which carried him through life. ‘I reckon fortitude’s the biggest thing a man can have,’ he wrote. ‘Just to go on enduring when there’s no guts or heart left in you.’ No wonder his favourite book was The Pilgrim’s Progress. He loved its plain narrative, ‘its picture of life as a pilgrimage over hill and dale’. It’s a summary that could double as a description of his own writing.

We drive on, through fields and forests, past the ruins of ancient hilltop forts, to Broughton, the village where the young Buchan spent his summers with his grandparents. Their farmhouse is just as Buchan described it, ‘at the mouth of a shallow glen, bounded by high green hills’. Today Deborah lives in this historic house with her husband Lord Stewartby — like Buchan, a former Tory MP. I am shown the room where Buchan used to write, and where his parents were married. As we drink tea in the kitchen, a dog dozing beside the stove, Buchan’s friendly ghost feels very close at hand.

Deborah drives me back to Waverley to catch the last train to London. As Buchan’s Borderland fades into bland suburbia, I recall something he wrote in his autobiography shortly before he died: ‘The Border hills were my own possession, a countryside in which my roots ran deep.’ Like so many of his countrymen, Buchan was a Scottish patriot and an ardent unionist. ‘The narrower kinds of fanaticism, which have run riot elsewhere in Scotland, rarely affected the Borders,’ he wrote in 1940. His lush Border Heimat is now the only Conservative seat in Scotland. I wonder what he’d think?

As my train heads south, I take up The Thirty-Nine Steps again for the umpteenth time. After my literary outing, Buchan’s evocation of the Lowlands seems more vivid than ever. He himself called the book a ‘shocker’. I reckon it’s actually a poem in disguise. ‘I always felt a little ashamed that profit should accrue from what had given me so much amusement,’ he reflected towards the end of his busy life. ‘I had no purpose in writing except to please myself; and even if my books had not found a single reader I would have felt amply repaid.’