If almost 800 pages are necessary to capture the essence of Norman Lewis's long and adventure-filled life, then an 800-word review can scarcely begin to do justice to Julian Evans's biography of this highly regarded and important, if often overlooked, writer. Semi-Invisible Man is a magnificent book, not only for its meticulous, spirited and colourful depiction of Lewis and his work (it could hardly fail to be vibrant, given Lewis's lust for excitement), but also for Evans's stimulating and highly welcome meditations throughout on the nature of biography, the need for stories and, ultimately, on our relationship with truth itself.

From early beginnings in his late twenties, and continuing well into his nineties, Lewis wrote almost 30 books - both fiction and non-fiction - as well as numerous magazine articles, often being one of the first to bring public attention to the plight of indigenous peoples around the world. One of these, published by the Sunday Times in 1969, led directly to the founding of Survival International. However, he is perhaps best remembered for his travel writing, with Naples '44, Voices of the Old Sea and A Dragon Apparent regarded as classics of the genre. His last work, The Tomb in Seville, was published in 2003, just four months after his death.

"This is a biography by someone who dislikes biography about someone who disliked exposure," Evans tells us in his prelude. After turning the chance down twice, he decided in the end to write the book to prevent anyone else from doing so, "given my intense dislike of some of the ways in which biography is written". And his principal focus was always to understand why Lewis wrote in the first place. Immediately the reader's fears that this might be yet another scandal-seeking, "truth-revealing" investigation are allayed. Lewis is in safe hands, his dignity intact.

Evans was Lewis's friend and editor during the latter part of his life (hence his familiar use of "Norman" when referring to him; the title of the book comes from a dedication Lewis wrote in Evans's copy of To Run Across the Sea), yet there is no sense of anything missed or glossed over here. We learn everything any other bio grapher would have told us - about his life as a dandy, celebrated photographer and successful businessman, racing driver, soldier and spy, as well as, more famously, a traveller and writer - but also about Lewis's complicated love life, his eccentric fathering (he taught his children how to poach) and his drug-taking (Benzedrine). It is noteworthy, however, that although no details are spared, any delving into Lewis's less attractive traits is done with an unfashionable delicacy; always respectful, never scurrilous. Lewis was known for his politeness towards others; it is only fitting that a study of his life should mirror that in its treatment of him.

Another strength of the book is its refusal to use the biographer's advantage of hindsight to find shape or patterns to Lewis's life where there are none. As far as is possible, Evans tells Lewis's story from his subject's perspective, events crashing into the narrative as chaotically as they occurred at the time. The result is to create a multidimensional picture of the man, with all the textures and contradictions of his personality: showy yet self-effacing, affectionate and cold, easily bored yet never boring. This may be a personal, sometimes subjective view of his life, as Evans says, yet the sense is of Lewis himself appearing very clearly from the page, not the biographer's image of him.

What is most refreshing to discover, however, is that Evans treats apparent discrepancies between certain events in Lewis's life and his later recounting of them in his books and other writings with great sensibility. "He was a writer after all, a writer of the Romantic or at least subjective stamp that realises meaning and truth are a scattered dissemination of signifiers, and that the writer's job is to take advantage of that," he says.

Taking up the theme later on when discussing differences between two accounts of a dinner in Algeria during the war - one Lewis's, the other a colleague's - he adds: "The question usually posed about modern dramatisations of 'real' events is always the wrong one. The important question is not 'Is it true - good - or invented - bad?' but 'What quality of meaning does it offer?'" Lewis's account almost certainly has elements of fabrication, but is the better for it, providing meaning "because of its distortion".

There is plenty of evidence of a storyteller's licence being used throughout Lewis's writing career, and in the hands of a less subtle biographer he would have been accused at the very least of "embellishment", at worst of lying. But as Evans points out, "a writer's lie is more satisfying than reality's truth, should that be available anywhere". It is no surprise that Lewis's favourite film was Kurosawa's Rashomon, the story of a rape and a murder told from four very different points of view. Lewis was an intelligent writer searching for meaning in a world devoid of definitive accounts or interpretations of "truth". That is why he is so admired, and why his books will survive. In Evans he has been given the biographer he most deserves. Semi-Invisible Man is designed to stimulate readers to reach out and discover (or rediscover) Lewis for themselves. It not only succeeds in that, but is a triumph in almost every regard.