The explorers who spent the 18th and 19th centuries searching for the source of the river Nile battled great obstacles, but they had an advantage: They knew the end justified their search for the beginning.

Explorers of new fiction have no such knowledge, particularly when the author is new as well. So readers of "The True Sources of the Nile," the deep and flowing first novel by Sarah Stone, can be excused if they wonder early on if their effort will be rewarded.

Stone sets her story half in Burundi and the other half in the Bay Area, and it takes her time to lay her groundwork. Her linchpin is Anne, a Californian who has fled from home with the excuse of saving the world. After a few months in Bujumbura, Burundi's capital, she encounters Jean-Pierre, a tall and graceful official in the Interior Ministry, and is transformed. "I wouldn't say it was love at first sight. I wouldn't say I even felt lust, not then. There was something about him that made me happy, immediately . . . ."

Soon enough, though, Anne's bliss is interrupted by word from home that her mother is dying, and though she would have stayed if she thought she could live with the guilt, she dutifully races home. While she's there, she's plunged back into the sibling rifts and family resentments she'd left behind, and then it's back to Burundi.

For almost half the book, that seems to be it: biracial love in exotic Africa, balanced by crisis at home. It's fine if you like that sort of thing.

Then the blood starts to flow.

Anne, her boss at a human-rights agency, and Charles, their Burundian aide, are returning from a trip in the interior one day when they encounter a roadblock. The whites can pass, but Charles must stay, and only quick thinking by Anne gets him through. "Ten minutes later we came around a bend in the road and were in another world. Suddenly there were bodies beside the road, bodies in the ditches, people running after us with their hands held out, some of them bleeding. We couldn't encompass it at first, couldn't believe what we were seeing. It had been such an ordinary day."

Immediately, radically, the foundations of their lives change, and so, of course, does the novel. Not only the plot but the pace changes, for the quicker and better. Scenes of massacre, and one in particular, flash before the windows of their Land Cruiser as they career back to the capital.

By the time they return to its now-deserted streets, Anne is frantic about Jean-Pierre and wants to set out immediately to find him, but her boss heads for the US embassy, where Anne reluctantly takes shelter with other expats. During the one hour she's allowed, under escort, to get belongings from her house, Jean-Pierre finds her, but instead of relief, she gets only more bad news: Members of his family, to whom she had grown close, are missing and presumed victims of the slaughter. Stone's portrait of how Anne deals with the implosion of her world - the carnage she witnessed on the road, her fear over the fate of Jean-Pierre's family, the loss of civil order - makes up one of the novel's most compelling passages.

Another compelling portrait is of Burundi itself. As Stone describes it, generations of Hutu-Tutsi strife have left the people both weary and wary, so that a veil hangs over every interaction: Burundians are "a people so hidden, angry, frightened, reserved, andyet they have these smiles, as if giving you everything, an offering of piercing sweetness."

Comfort isn't a Burundian concept, and neither is solitude. Little is explained, and yet everyone seems to know everyone else's business; it is Burundians whom Anne has never met and will never see again who complete the destruction of the life she had known in Africa, a blow that comes just when Anne is adjusting to reordered life.

Though the scale is different, Stone carries this obliqueness to California, where Anne retreats when evacuation can be carried out safely; plenty goes unsaid within the walls of her family home, between sisters and particularly between mother and daughters.

There is obliqueness even in the title: Though Burundi is home to the remotest headwaters of the Nile, there is no discussion of the river in the story. But having taken in all that Stone does offer, that's of little import. Deft perceptions and deep emotions, set against a real world most Westerners know little about, create a pleasing and promising first novel.