Book of a lifetime: Greenmantle, By John Buchan

I suffered from acute asthma as a child. Until I was 11 or so, there was no effective medication for the ailment, so I spent a fair bit of time off school. Adventure stories, read propped up in bed, provided my escape from tedium, and the spoonfuls of sticky malt I had to swallow to "build me up". I read everything from The Eagle of the Ninth to The Silver Sword to John Buchan's The 39 Steps – but it was another Buchan novel, Greenmantle, that sent me on a lifetime's flight of fantasy.

A ripping yarn by any standards, Greenmantle is set across two action-packed months during the First World War. At the outset, the suave soldier-spy Richard Hannay – a kind of Edwardian James Bond figure - is convalescing after a typically heroic stint on the Western Front. Hannay and his admirable sidekick Sandy Arbuthnot are summoned by the Foreign Office's senior intelligence commander, Sir Walter Bullivant. Buchan's nomenclature, incidentally, is peerless; from maverick Boer guerillas (Piet Pienaar) to icily sinister Prussian overlords (General Ulrich von Stumm) and femmes fatales (Hilda von Einem), he names his characters as pertly as he draws them.

Bullivant briefs Hannay that Turkish seditionaries are planning to whip up discontent among Muslim nations across Asia Minor and into North Africa. An Islamic uprising will create a major headache for Britain, and a diversion the Turks' German allies can exploit. Our dapper hero has only weeks to foil this dastardly plot. What ensues is a wholly absurd and phenomenally enjoyable romp across half the world as Hannay, Sandy and Pienaar split up and use their ingenuity to get behind enemy lines and defy the Young Turks' rebellion.

Greenmantle is the first book I read with both an atlas and an encyclopedia to hand, as Hannay gives a succession of shady ne'erdowells the slip on foot, by sea, on a wild mustang – even by barge. The book gave me a taste for high-energy crime and action thrillers but, in doing so, it brought a secret and seductive world to life, too.

With ripe evocations of Vienna, Budapest and Belgrade as Hannay takes a slow boat down the Danube to Constantinople, Greenmantle remains one of the most exotic novels I've ever read. As a convalescing 11-year-old, I could envisage the smells and sights and sounds of those mysterious cities, and I was desperate to visit every one. It's a special sort of book that can fire your imagination and transport you to worlds you've never known, but Greenmantle continues to take me on a trip, every time I read it.

Kevin Sampson's 'The Killing Pool' is published by Jonathan Cape