The truth is, if old Major Dover hadn't dropped dead at Taunton races Jim would never have come to Thursgood's at all. He came in mid-term without an interview, late May it was though no one would have thought it from the weather, employed through one of the shiftier agencies specialising in supply teachers for prep schools, to hold down old Dover's teaching till someone suitable could be found. 'A linguist,' Thursgood told the common room, 'a temporary measure,' and brushed away his forelock in self-defence. Priddo.' He gave the spelling P-R-I-D' - French was not Thursgood's subject so he consulted the slip of paper - 'E-A-U-X, first name James. I think he'll do us very well till July.' The staff had no difficulty in reading the signals. Jim Prideaux was a poor white of the teaching community. He belonged to the same sad bunch as the late Mrs Loveday who had a Persian lamb coat and stood in for junior divinity until her cheques bounced, or the late Mr Maltby, the pianist who had been called from choir practice to help the police with their enquiries, and for all anyone knew was helping them to this day, for Maltby's trunk still lay in the cellar awaiting instructions. Several of the staff, but chiefly Marjoribanks, were in favour of opening that trunk. They said it contained notorious missing treasures: Aprahamian's silver-framed picture of his Lebanese mother, for instance; Best-Ingram's Swiss army penknife and Matron's watch. But Thursgood set his creaseless face resolutely against their entreaties. Only five years had passed since he had inherited the school from his father, but they had taught him already that some things are best locked away.

Jim Prideaux arrived on a Friday in a rainstorm. The rain rolled like gun-smoke down the brown combes of the Quantocks, then raced across the empty cricket fields into the sandstone of the crumbling facades. He arrived just after lunch, driving an old red Alvis and towing a second-hand caravan that had once been blue. Early afternoons at Thursgood's are a tranquil time, a brief truce in the running fight of each school day. The boys are sent to rest in their dormitories, the staff sit in the common room over coffee reading newspapers or correcting boys' work. Thursgood reads a novel to his mother. Of the whole school therefore only little Bill Roach actually saw Jim arrive, saw the steam belching from the Alvis' bonnet as it wheezed its way down the pitted drive, windscreen wipers going full pelt and the caravan shuddering through the puddles in pursuit.

Roach was a new boy in those days and graded dull, if not actually deficient. Thursgood's was his second prep school in two terms. He was a fat round child with asthma and he spent large parts of his rest kneeling on the end of his bed, gazing through the window. His mother lived grandly in Bath; his father was agreed to be the richest in the school, a distinction which cost the son dear. Coming from a broken home Roach was also a natural watcher. In Roach's observation Jim did not stop at the school buildings but continued across the sweep to the stable yard. He knew the layout of the place already. Roach decided later that he must have made a reconnaissance or studied maps. Even when he reached the yard he didn't stop but drove straight on to the wet grass, travelling at speed to keep the momentum. Then over the hummock into the Dip, head first and out of sight. Roach half expected the caravan to jack-knife on the brink, Jim took it over so fast, but instead it just lifted its tail and disappeared like a giant rabbit into its hole.

The Dip is a piece of Thursgood folklore. It lies in a patch of waste land between the orchard, the fruithouse and the stable yard. To look at, it is no more than a depression in the ground, grass-covered, with hummocks on the northern side, each about boy-height and covered in tufted thickets which in summer grow spongy. It is these hummocks that give the Dip its special virtue as a playground and also its reputation, which varies with the fantasy of each new generation of boys. They are the traces of an open-cast silver mine, says one year, and digs enthusiastically for wealth. They are a Romano-British fort, says another, and stages battles with sticks and clay missiles. To others the Dip is a bomb- crater from the war and the hummocks are seated bodies buried in the blast. The truth is more prosaic. Six years ago, and not long before his abrupt elopement with a receptionist from the Castle Hotel, Thursgood's father had launched an appeal for a swimming pool and persuaded the boys to dig a large hole with a deep and a shallow end. But the money that came in was never quite enough to finance the ambition, so it was frittered away on other schemes, such as a new projector for the art school, and a plan to grow mushrooms in the school cellars. And even, said the cruel ones, to feather a nest for certain illicit lovers when they eventually took flight to Germany, the lady's native home.

Jim was unaware of these associations. The fact remains that by sheer luck he had chosen the one corner of Thursgood's academy which as far as Roach was concerned was endowed with supernatural properties.

Roach waited at the window but saw nothing more. Both the Alvis and the caravan were in dead ground and if it hadn't been for the wet red tracks across the grass he might have wondered whether he had dreamed the whole thing. But the tracks were real, so when the bell went for the end of rest he put on his Wellingtons and trudged through the rain to the top of the Dip and peered down and there was Jim dressed in an army raincoat and a quite extraordinary hat, broad-brimmed like a safari hat but hairy, with one side pinned up in a rakish piratical curl and the water running off it like a gutter.

The Alvis was in the stable yard; Roach never knew how Jim spirited it out of the Dip, but the caravan was right down there, at what should have been the deep end, bedded on platforms of weathered brick, and Jim was sitting on the step drinking from a green plastic beaker, and rubbing his right shoulder as if he had banged it on something, while the rain poured off his hat. Then the hat lifted and Roach found himself staring at an extremely fierce red face, made still fiercer by the shadow of the brim and by a brown moustache washed into fangs by the rain. The rest of the face was criss-crossed with jagged cracks, so deep and crooked that Roach concluded in another of his flashes of imaginative genius that Jim had once been very hungry in a tropical place and filled up again since. The left arm still lay across his chest, the right shoulder was still drawn high against his neck. But the whole tangled shape of him had stiffened, he was like an animal frozen against its background: a stag, thought Roach on a hopeful impulse, something noble.

'Who the hell are you?' asked a very military voice.

'Sir, Roach, sir. I'm a new boy.'

For a moment longer, the brick face surveyed Roach from the shadow of the hat. Then, to his intense relief, its features relaxed into a wolfish grin, the left hand, still clapped over the right shoulder, resumed its slow massage while at the same time he managed a long pull from the plastic beaker.

'New boy, eh?' Jim repeated into the beaker, still grinning. 'Well that's a turn up for the book, I will say.'

Rising now, and turning his crooked back on Roach, Jim set to work on what appeared to be a detailed study of the caravan's four legs, a very critical study which involved much rocking of the suspension, and much tilting of the strangely garbed head, and the emplacement of several bricks at different angles and points. Meanwhile the spring rain was clattering down on everything: his coat, his hat and the roof of the old caravan. And Roach noticed that throughout these manoeuvres Jim's right shoulder had not budged at all but stayed wedged high against his neck like a rock under the mackintosh. Therefore he wondered whether Jim was a sort of giant hunchback and whether all hunch backs hurt as Jim's did. And he noticed as a generality, a thing to store away, that people with bad backs take long strides, it was something to do with balance.

'New boy, eh? Well I'm not a new boy,' Jim went on, in altogether a much more friendly tone, as he pulled at a leg of the caravan. I'm an old boy. Old as Rip Van Winkle if you want to know. Older. Got any friends?'

'No, sir,' said Roach simply, in the listless tone which schoolboys always use for saying 'no', leaving all positive response to their interrogators. Jim however made no response at all, so that Roach felt an odd stirring of kinship suddenly, and of hope.

'My other name's Bill,' he said. 'I was christened Bill but Mr Thursgood calls me William.' 'Bill, eh. The unpaid Bill. Anyone ever call you that?'

'No, sir.'

'Good name, anyway.'

'Yes, sir.'

'Known a lot of Bills. They've all been good 'uns.'

With that, in a manner of speaking, the introduction was made. Jim did not tell Roach to go away so Roach stayed on the brow peering downward through his rain- smeared spectacles. The bricks, he noticed with awe, were pinched from the cucumber frame. Several had been loose already and Jim must have loosened them a bit more. It seemed a wonderful thing to Roach that anyone just arrived at Thursgood's should be so self-possessed as to pinch the actual fabric of the school for his own purposes, and doubly wonderful that Jim had run a lead off the hydrant for his water, for that hydrant was the subject of a special school rule: to touch it at all was a beatable offence.

'Hey you, Bill. You wouldn't have such a thing as a marble on you by any chance?'

'A-sir-what-sir?' Roach asked, patting his pockets in a dazed way.

'Marble, old boy. Round glass marble, little ball. Don't boys play marbles any more? We did when I was at school.'

Roach had no marble but Aprahamian had had a whole collection flown in from Beirut. It took Roach about fifty seconds to race back to the school, secure one against the wildest undertakings and return panting to the Dip. There he hesitated, for in his mind the Dip was already Jim's and Roach required leave to descend it. But Jim had disappeared into the caravan, so having waited a moment Roach stepped gingerly down the bank and offered the marble through the doorway. Jim didn't spot him at once. He was sipping from the beaker and staring out of the window at the black clouds as they tore this way and that over the Quantocks. This sipping movement, Roach noticed, was actually quite difficult, for Jim could not easily swallow standing up straight, he had to tilt his whole twisted trunk backward to achieve the angle. Meanwhile the rain came on really hard again, rattling against the caravan like gravel.