He could have been the great English Modernist. At 29, ambitious and talented, he had already earned the friendship of Picasso and the respect of the Paris avant garde. Then, in 1930, Christopher Wood threw it all away. By RICHARD INGLEBY
In the Tate Gallery Archive, among the neatly catalogued boxes of letters, diaries and photographs - the usual artefacts of art history - there are five pages of close-typed paper detailing the movements of a man, identified only as W, on the 20 and 21 August, 1930: "W arrived at the Pier Hotel, Yarmouth, Isle of Wight about 11 o'clock on 20 August and was allotted room number nine. He stated he was going to stay for two days. He had with him two suitcases (one of them blue) and three large packets or holders containing, it was understood, pictures. He went to his room with the porter, came down within five minutes and had two whiskies and soda and a sandwich. He then went out. At about 12.40 he came in again, had a whisky and soda at the bar."

The document is a private detective's report compiled from eye-witnesses, and it makes gripping reading. W continues to order whiskies and soda at all times of the day and night, he meets men in cars that are unrecognised by anyone in the vicinity, he stays out all night and then changes his story as to where he spent it, he keeps a six-chamber revolver in his overcoat pocket and he leaves the island by the morning boat on Thursday, 21 August. By mid-afternoon, W is dead.

The report appears among the papers of a woman named Frosca Munster, a Russian emigree who lived in Paris in the Twenties, but it was commissioned by the artists Ben and Winifred Nicholson to help explain the circumstances surrounding the death of their greatest friend, the English painter Christopher Wood - the W who appears in the detective's report. Frosca Munster was Wood's last lover.

The death of Christopher Wood, aged 29, is an unsolved mystery in the story of British painting between the wars, and the findings of the Nicholson's detective only deepen the mystery. It was a sad and muddled end for a man who had set out nine years earlier with a very specific intention. Wood had arrived in Paris in 1921, and soon struck up a friend-ship with Tony Gandarillas, a wealthy, bisexual, opium-smoking dilettante loosely attached to the Chilean Embassy, who supported him financially for most of the decade. In October of that year, six months after his arrival in Paris, Wood wrote to his mother in defence of what she took to be his dissolute lifestyle: "Dearest mother, you ask me what I am going to do: I have decided to try and be the greatest painter that has ever lived". For an ambitious young man on the threshold of his career, this was a natural enough desire: anything less and he would not have been trying hard enough. However, what marked Christopher Wood out from his contemporaries was that, for a few years in the middle of the Twenties, it looked as if something of this extravagant ambition were close to coming true. Not necessarily to be the greatest who had ever lived, but to compete, at the tender age of 25, with the men he had grown up regarding as the greatest English artists of his day. By the time he met Ben Nicholson in 1926, Wood had yet to have an exhibition, or, indeed, to sell more than a handful of pictures, but he had already talked his way to the distinction of being the only English painter ever to design for Diaghilev's Russian Ballet, a commission won in the face of competition from both Wyndham Lewis and Augustus John.

The Twenties were not a high point in the history of British art, but in a quiet way they were crucial years which laid the ground for the advances that followed in the early Thirties. The formation of the Seven & Five Society set the tone. They were a disparate group, originally envisaged as an annual exhibiting society of seven painters and five sculptors, although their first exhibition in April 1920 listed a total of 18 members who had little in common beyond a desire to find shelter from the storm of ideas blowing from Paris. The manifesto which they published in their first catalogue in 1920 reads like a lesson in wilful restraint: "The Seven & Five are grateful to the pioneers but feel that of late there has been too much pioneering along too many lines in altogether too much of a hurry."

Under the leadership of Ben Nicholson in 1926, the mood and membership of the Seven & Five began to change and Christopher Wood was one of his first conscripts. By 1927, they were being hailed by the critic Frank Rutter in the Times as: "the most important group of young artists with advanced ideas". In some respects, the progress of the Seven & Five plots the course of English painting in the Twenties and early Thirties. They were slow starting and yet, in the space of 15 years, their annual exhibition evolved from still life and landscape pictures with titles such as The Woodcutter's Cabin and Where the Thrushes Sing to the sophistication of a Ben Nicholson white abstract relief.

Christopher Wood played an important role in this decade of gentle transformation. At a time of relative cultural isolation on this side of the Channel, Wood brought to his friendship with Ben Nicholson in particular, and to English art in general, the direct experience of the European avant-garde. As his contemporary, the novelist Anthony Powell, has written: "He was the only English artist found acceptable in the Paris monde of Picasso and Cocteau, a convenient bisexuality being no handicap in that particular sphere." Cocteau himself described Wood as the sort of man whom, "if I didn't know already, I would want to, having seen his pictures... Before the canvases you don't think, you live. No subtle problem poses itself here. A bunch of flowers is a bunch of flowers, smell it. A street is a street, walk down it." Cocteau makes the pictures sound deceptively simple, but it was a simplicity born of hard work and careful learning. The effect is, as Wood described it, the appearance of having got there by accident, but in reality his best work and his unique way of looking at the world were the product of a delicate balance between naivety and sophistication. It was this balance, and the quality that sprang from it of finding surprise in ordinary things, that won Wood the friendship and admiration of artists as diverse as Jean Cocteau, Picasso and Ben Nicholson who wrote, shortly after Wood's death: "When you walk in the country with Christopher Wood, the fields become a much more intense green and in London the buses a much more pungent red... I miss him more than I can say. I could have parted with almost anyone but him."

Two days before his tragic death, Wood left the Gare du Nord in Paris on a boat train bound for Le Havre. His plan was to take the night crossing to Southampton and then the train up to London to meet a friend whose gallery was to open in September that year with an exhibition of Wood's recent work. On the boat he seems to have seen someone he recognised, or who recognised him. Someone (according to a version of events which originated from Wood himself) who threatened him. Why and with what is not known, although Wood's opium smoking, a long-standing habit which had by 1930 become an addiction, and his homosexual past make blackmail a likely possibility.

When the boat docked at Southampton, he telephoned his mother and sister and arranged to meet them for lunch in Salisbury the following day. Wood then caught the ferry to Yarmouth, where the detective's report picks up his trail. According to the waiter on duty at the Pier Hotel on Thursday, 21 August, Wood walked into the dining room a few minutes after 6.30am. He asked (predictably) for a whisky and soda, but was told that the bar wasn't open. A little over two hours later, Wood caught the Lymington Ferry and from there took the train to Salisbury, where he lunched with his family before returning to the station to take the train up to London. Wood walked onto the platform, bought a book from a stall and sat down on a bench to read. He opened and shut the book several times but, unable to concentrate on the words, he began to pace up and down the platform. At 2.10, just as the train known as the Atlantic Coast Express was pulling into the station, Wood threw himself onto the tracks. He died instantly.

The jury at the inquest returned a verdict of suicide while of unsound mind, and the coroner remarked that in these instances one searches for a motive but that here there appeared to be none - "the man was clearly out of his senses". All that the coroner could discover was that Wood had arrived that morning from the South Coast and had spent an hour or two at the County Hotel before meeting his mother. Witnesses reported his manner as strange, but nothing was said or done that could shed any light on his subsequent suicide. It was left to Ben and Winifred Nicholson to discover more but, unlikely as it seems, having received and read the detective's report, they decided to call off their investigation. For a brief period in the late Twenties, their lives and work had been intricately bound, but Wood's death marked an end to the way things had been. By the autumn of 1930, Ben's work was moving towards a world of cool, clean abstraction where it is hard to imagine Christopher Wood could have followed. Nicholson went on to play a leading role in defining Modernism in this country, but, if it had been him who had died in August 1930, he would be no more than a footnote to our artistic history: the son of Sir William and husband of Winifred. When Wood and Nicholson exhibited together in Paris in May 1930, it was Wood's pictures which sold, albeit to a friend, and Wood who was hailed by the press in both Paris and London while Nicholson was universally ignored.

The picture thought to be Wood's last (painted in the month of his death), Zebra and Parachute, with its echoes of the sort of Surrealism practised by de Chirico, offers a clue to the road he might have taken, but more conclusively it shows something of the way he was feeling. It is a lonely, rather melancholic image that seems to acknowledge its status as an end- picture in its strange iconography. A listless, perhaps dead, figure drops to earth behind the Villa Savoye - Le Corbusier's then unfinished villa on the edge of Paris - his red-and-yellow parachute like a sun setting on a building that was itself a symbol of European Modernism.

`An English Painter' by Richard Ingleby is published by Allison & Busby on 29 May at pounds 25. An exhibition of Christopher Wood's paintings is at the Fine Art Society, 148 New Bond Street, London W1, from Monday