SPRING IS HERE, which in recent years has come to mean not merely green things and baseball and other familiar delights. Of late it has also come to mean the unexpected appearance of sublimely accomplished works of fiction by writers previously unknown. Three years ago it was A Good Man in Africa, by William Boyd; two years ago, Here to Get My Baby Out of Jail, by Louise Shivers; a year ago, I Wish This War Were Over, by Diana O'Hehir; and now, to provide delicious accompaniment for the crocuses and daffodils of 1985, Sour Sweet, by Timothy Mo.

Unlike these three other books of spring, Sour Sweet is not a first novel; a previous one, The Monkey King, was published in England a dozen years ago. But so far as American readers are concerned it might as well be, and they can look forward to reading it with the same pleasurable sense of discovery that any genuinely rewarding first novel offers. Sour Sweet is, on every level that really matters, a work filled with wonders, surprises and rewards -- a novel that, at the risk of using a word cheapened by familiarity and abuse, can only be described as enchanting.

Timothy Mo is the son of an English woman and a Cantonese man, and in this novel he has chosen to write about the clash of those cultures from which he himself has been formed. He has settled a little Chinese family in London in the early 1960s, found a house for them in a most unprepossessing neighborhood, set them up in a carryout-Chinese- food business, and let their lives unfold in ways that are often unpredictable but always illuminating. In certain respects Sour Sweet is, as its title suggests, a sad book, for life is not always easy for the Chens and in the end something terrible, though not insuperable, happens to them; but far more than that it is a wry and joyful book, packed with life and loaded with uproariously funny scenes.

At first there are three of them: Chen, the husband, a stolid and rather taciturn man who works as a waiter in a restaurant in London's Chinese quarter; Lily, his wife, a woman of demure demeanor but great willpower and inner strength; Man Kee, their infant son, "whose persistent demands, irregular tantrums, and constant need for attention and physical reassurance from his supporting cast of adults far exceeded any ever made by the placid and equable Chen." Soon they are joined by Mui, Lily's spinster older sister, who at first refuses to leave their flat and forms, from incessant watching of television, dire impressions of the country in which she now lives: "She gave the characters names of her own devising: Boy, Hair-net, Drinker, Cripple, Crafty, Bad Girl. The composite picture she was able to glean of the British population was an alarming one."

But presently Mui, like her sister and brother-in-law and nephew, moves out into this strange new world and begins to make her accommodations with it. For all the members of the family -- and eventually for Chen's elderly father, who comes from China to live with them -- this is the principal business at hand, and the principal theme of Mo's novel. But in choosing to approach his subject in this way, he has turned a witty, imaginative and wholly successful twist on what has become a familiar 20th-century genre. In the clash-of-cultures novel, whether written by Evelyn Waugh or V.S. Naipaul or Paul Theroux, it is the Westerner who ventures out into the exotic and unknown; but in Sour Sweet it is the exotic and unknown that ventures into the West, which gives the clash an entirely different resonance even as the fundamental nature of that clash remains the same.

What happens to the family, in brief, is that troubles back in China force Chen to take a substantial loan so he can send money to his relatives there. This loan he acquires through an unscrupulous representative of a Triad, a "family" based in Hong Kong that is part Mafia and part benevolent ward boss. Chen fears the Triad, and decides to leave the Chinese quarter in the somewhat unrealistic hope that it will forget about him. He and Lily -- who is ambitious and has long wanted him to go out on his own -- find a house in an industrial area, hard against a car-repair shop, and open business there. In the kitchen Chen cooks, while in the front room Lily and Mui serve the customers:

"The food they sold, certainly wholesome, nutritious, colorful, even tasty in its way, had been researched by Chen. It bore no resemblance at all to Chinese cuisine. They served from a stereotyped menu, similar to those outside countless other establishments in the UK. The food was, if nothing else, thought Lily, provenly successful: English tastebuds must be as degraded as their care of their parents; it could, of course, be part of a scheme of cosmic repercussion. 'Sweet and sour pork' was their staple, naturally: batter musket balls encasing a tiny core of meat, laced with a scarlet sauce that had an interesting effect on the urine of the customer the next day."

Observing her customers Lily remarks to herself that "there was no question how superior Chinese people were to the foreign devils," and furthermore: "They all looked the same to her. And how quickly their pink skins aged. How few types of face there were compared to the almost infinite variety of interesting Cantonese physiognomies: rascally, venerable, pretty, raffish, bumpkin, scholarly." While the English wallow in "lurid orange sweet and sour pork with pineapple chunks," the Chinese in their greater wisdom taste the delights of "white, bloody chicken and yellow duck's feet." These lapses in British taste are all about them, but Lily and Chen can only sigh, comment upon the great mystery of them, and go about the business of their lives.

WHEN IT COMES to the education of Man Kee, though, England presents grave difficulties. At the age of 51/2 he goes off to a British school, but to Lily it is entirely unsatisfactory; he seems to do nothing all day except play, and for lunch is served "mince, jam tart and custard," which into the bargain he has the effrontery to like. This is all wrong: "Basically, Lily's philosophy of education was simple: it didn't matter what Man Kee studied so long as he didn't like it. The main purpose of his lessons was to train his character, foster diligence, teach him discipline and obedience. Acquiring knowledge was almost secondary to this. That was what pupils learned at Ling Nan primary and middle school, Stubbs Road, Hong Kong -- possibly the best school in the world."

So once a week Lily packs Man Kee off to a Chinese school for immersion in the eternal verities, but she can't escape the inevitabe: England is having its way with Man Kee, just as it is with all of them. And the way it is having is not, Lily must reluctantly acknowledges (if to no one save herself), entirely bad. They acquire a battered old van, for example, at the operation of which Lily soon proves to be gleefully adept. Slowly, cautiously, they make friends with Mr. Constantinides, the operator of the car shop, and with the truckdrivers who stop there for service. Mui, in particular, bursts forth from her cocoon and becomes positively cross-cultural, with results that often shock the ardently traditionalist Lily.

While all of this goes on, there is yet another story, that of the gradual evolution of the marriage of Lily and Chen. It begins, as so many marriages do, in mutual ignorance of each other's essential nature, but over the years it slowly ripens, often in ways that surprise the parties to the marriage as much as they do the reader. Confronted with the discovery that Lily has somehow managed to skim money off the business' small profits, Chen enters terra incognita: "Whole new regions of the female psyche, not only unexplored but their existence hitherto unsuspected, opened before him." It is no less surprising to Lily that when she masters the motor vehicle that had defeated Chen's best efforts, he happily accepts her proposal of "a jaunt to the sea" and revels in "her mastery of this new skill." The happy result of all of this is that a man and woman who had at first scarcely known each other, now, though they are inadequate at expressing it, have come to love each other.

If anything, indeed, Sour Sweet is a book about love. Its humor comes from the confrontation of alien cultures, but its great tenderness comes from the depiction of a family that is in this thing together: "So, again, the household (that amoeba), presented with change and challenge, shuddered like jelly on impact with the obstacle but jelly-like suffered no damage, poured itself around the problem, dissolved what it was able to and absorbed what it could not. And went on its amoeba way." Nothing about the novel is so clear as that Timothy Mo deeply loves these eccentric and spunky people he has created. He has given them qualities that are distinctly Chinese, and qualities that are distinctly human, and what he has to tell us is that the two are exuberantly the same. His book -- a work of absolute originality, written with beauty and quiet energy -- is a wonder. It is also entirely irresistible.