THE THOUGHT ARISES, as a quite unexpected result of reading this collection of interrelated short stories, that there may be no greater challenge to a writer of fiction than the depiction of two people falling in love. The lovers' passion for each other may be grand or subdued, their progress toward a lifetime together may be stormy or sedate, but none of that matters in the least if the writer fails to persuade the reader that their attraction to each other is plausible; in effect, the writer must make the reader, as well as his characters, fall in love. In art as in life, that can be a tricky business.

Certainly it's a business that quite thoroughly takes the measure of Paul Theroux in the last three stories of The London Embassy. After establishing himself in the previous 15 stories as a person of considerable detachment, solitariness and independence, the unnamed (until the last story) narrator suddenly decides to chuck it all and volunteer for domestic bliss:

"I had never thought that I would fall in love with anyone. Then it seemed to me that living with another person was the only thing that mattered on earth, that this solitary life I had been leading was selfish and barren--and turning me into a crank--and that Flora was my rescuer. Part of love was bluff and fumbling and drunkenness. I knew that--but it was the pleasant afterglow of moonshine. The other part of love was real emotion: it was stony and desperate; it made all lovers shameless; and it did not spare me. I was alive, I was myself, only when I was with Flora, and that was always too seldom."

All of which is well and good, except that the mantle of romance rests most uneasily upon Theroux's shoulders. He presents the reader with Flora, and he announces that the narrator is madly in love with her, but her appearance at the end of this little book is, in point of fact, a mere afterthought--a convenient device for tidying things up in the closing pages. Flora seems an attractive young woman, and an intelligent one, but it is not in the least way clear why she, as opposed to any of the other women who previously had attracted the narrator's attention, should be the one to put zing into the strings of his heart. We've hardly made her acquaintance, and suddenly there they are, tying the knot at the Chelsea Registry Office; it's too much too soon, and it isn't even remotely believable.

To say this isn't merely to harp on what may seem a relatively minor point; it is to emphasize that in Theroux's cool, clinical, worldly fiction a romance such as this seems somehow incongruous, even gratuitous. Theroux is a writer of many virtues, but sentiment is not among them; when he attempts it, the primary impression he conveys is of contrivance. At portraying the dark and ludicrous sides of life he is quite nearly as skilled and subtle as his master, Graham Greene; yet it is quite impossible to imagine Theroux inventing a romance as resonant as that which animates The Human Factor. The reasons for this probably defy explanation; yet the evidence of it is abundant in Theroux's large and rapidly growing body of published work.

Theroux is to be read, instead, for his unsparingly witty eviscerations of human vanity and pretense. At his best he is a merciless chronicler of the deceptions that people practice on themselves as well as others, of the nuances of affectation and self-display, of the implacable barriers that separate alien cultures. All of this he does in The London Embassy, just as he did six years ago in The Consul's File, the collection of stories to which it is the sequel.

In the first collection, the narrator is the American consul in the Malaysian provincial town of Ayer Hitam. Now he receives the long-awaited, long-desired promotion, to political officer at the embassy in London: "I had wanted London. In London I could meet anyone, do anything, go anywhere. It was the center of the civilized world, the best place in Europe, the last habitable big city. It was the first city Americans thought of traveling to--funny, friendly, and undemanding; it was every English-speaker's spiritual home. I had been intending to come here for as long as I could remember."

London proves, of course, somewhat more complex than our diplomat first imagines it to be; after a year at his post, just before his encounter with the hypnotic Flora, he concedes that "I had plenty of society but not much pleasure: it was not an easy city." Like countless thousands of Americans before him, he finds the reserve of the British to be chilling and daunting, even as it accommodates his own preference for privacy. In a fine story called "An English Unofficial Rose," he discovers that the civilities of his hosts can disguise a thoroughly cold-blooded predation; in "Fury," he learns through the experience of a young woman that the "good will toward Americans in London" should not be pressed too far.

There are other good things here. "Charlie Hogle's Earring," about a minor member of the embassy staff whose habits of attire become a source of discomfort, is a cannily described encounter between innocence and cynicism; the latter is victorious, needless to say, but it is an empty victory indeed. "Tomb With a View" finds, in the heart of London, an encounter between Western and Muslim cultures that is creepily revealing and true. "The Exile," though its conclusion is too pat for its own good, is a thoughtful examination of illusion and reality: "He was a public man; the facts are well known--but wait: it is the public men who have the darkest secrets. They have the deepest cellars and hottest attics, and they are consoled by blindness and locked doors. It is impossible to guess at what truly animates these people whose surfaces we seem to know so well, and there is nothing in the world harder to know than the private life of a public man."

But though there are indeed pleasures to be found in it, The London Embassy is on the whole a perfunctory performance. The Consul's File, similarly constructed and similarly slender, is greater than the sum of its parts; The London Embassy, if anything, is less. Perhaps this is because Theroux, though himself an eminently civilized writer, flourishes in the less civilized atmosphere of the undeveloped world; perhaps it is simply because he seems to insist on publishing at least one book a year and thus places excessive strain on his resources. Whatever the case, in The London Embassy he is largely marking time.