"The Dark Horse" belongs to an almost extinct species -- the nice, heartwarming novel. It is the kind of thing that was some writer's bread and butter in the heyday of the Saturday Evening Post, before television took over, standardized still further and ultimately debased our popular forms of narrative entertainment. If it had been published 30 or 40 years ago, it might have been made into a movie starring Bing Crosby. One wonders at the fate of such a sweet innocent in an age that has developed a taste for the more acrid flavors of Le Carre' and Kosinski, but Rumer Godden seems to be doing all right; 15 other books are listed facing the title page of "The Dark Horse," and while none has been a runaway best seller, they seem to have found a receptive readership.

What Rumer Godden offers in this instance includes elements familiar to her loyal followers -- notably memories from her youth in Calcutta in the 1930s. Against this background, she tells a story, based on a historical incident, involving nuns and horse racing, an alliance of various outsiders assaulting the stronghold of the colonial establishment -- and, of course, winning, as they always did in the wonderful, bygone world of Bing Crosby and the Saturday Evening Post.

The outcasts in the story are a curiously assorted lot. John Quillan, a horse trainer, was a promising young cavalry officer in the British colonial army until he made the mistake of marrying a Eurasian woman. Ted Mullins, middle-aged stable boy, was once a promising jockey, but he developed a drinking problem after his wife's death. Casimir Alaric Bruce Leventine is one of the richest men in Calcutta (his grandfather was "the man who first imported umbrellas into India"), but he is not invited to the city's best clubs because of mixed parentage.

The most curious person in this cast of characters (and a very real person indeed) is Dark Invader, a handsome, 2-year-old thoroughbred who performed spectacularly in his first race, was brutalized by a jockey and apparently decided that winning simply was not worth the effort and pain. "A splendid conformation's no good without guts," says his owner in England. "We have to face it. Darkie is a great big beautiful washout." And so Dark Invader is sold and shipped off to India, specifically to Leventine. Quillan becomes his trainer and Mullins his jockey in the race for the prestigious Viceroy's Cup, which Leventine wants to win for entree to the only segment of colonial society that interests him. Anyone, at this point, can see the outlines of a plot hinging on the question: Will Dark Invader win the race and make everybody happy?

But there is more to the novel than this simple plot. Besides the world of horse racing, Rumer Godden takes her readers into the world of the Sisters of Poverty, whose convent is near Quillan's stables. The sisters also have a horse, Solomon, old and no longer really equal to the job of pulling the heavy cart they use for their nightly collection of food scraps to feed the poor. When Solomon dies and Dark Invader wanders by accident into the convent grounds, the sub-plot begins to emerge: Will Dark Invader replace Solomon? The question in absurd; even if he were not enormously valuable, a thoroughbred race horse is unsuitable for such work by breeding and training; he simply could not do it. But the intrusion does give Mother Morag, the superior of the convent and an experienced horse trader, an opportunity for a bit of holy blackmail.

Behind her neat (perhaps slightly too neat) plotting, Rumer Godden has given her book a fair amount of substance. None of her characters is presented in great depth, but they are highly varied, ranging from Untouchable house servants to a Westernized maharajah who uses the nickname "Bunny," as well as an array of British colonial characters that almost amounts to a catalog. Her descriptions of Calcutta are excellent, particularly when the arrival of Mullins allows her to show the city through the eyes of a stranger. And the book has a constant undertone of society and the equally appalling attitudes of the colonial administrators.

The figure of Leventine is probably the most interesting in the book. A victim of colonial snobbery despite his enormous wealth, he is a sort of Scrooge, conducting his life as though it were a business, fairly but without any trace of generosity or emotional attachments. Only horses and racing seem to bring out any spark of humanity in him until his encounter with Mother Morag, which ultimately transforms his life by introducing him to the joy of giving. This crucial scene involves a neat and believable twist of plot and character, when the nun (a totally dedicated humanitarian) suddenly becomes a very sharp negotiator, beating the tough businessman at his own game.

"The Dark Horse" is not an important book, but it is well-crafted, constantly readable and well-balanced between substance and entertainment.