A Lost Life and a World That’s Passed Away : THE BOOK OF SECRETS by M.G. Vassanji; Picador $24, 339 pages

The First World War began in East Africa when an anthill opened fire on a British patrol. The British unit consisted of askaris, or African policemen. The anthill concealed a German askari; so did half a dozen bushes observed scuttling away. The encounter took place on what today is the border between Tanzania and Kenya. At the time, it separated a German colony from a British one.

In “The Book of Secrets,” the war is not so much a political event as a geological one. It is a tremor that displaces the vulnerable Indian population in East Africa; a forerunner to the earthquake 45 years later, when independence under a black majority would force many of them out altogether.

M.G. Vassanji introduces vividly suggestive incidents and characters, but seems unable to develop them or sometimes even to hold onto them. The book’s first half accumulates mystery and tension--the superior kind that consists of making us search not for an answer but, like “The Turn of the Screw,” for an incandescent question. The second half peters out in a narrative that is agreeable but increasingly scattered.

“Secrets” is told in the present day by Pius Fernandes. He is a Goan Indian who arrived in Dar es Salaam in the ‘30s and taught school until the ‘60s, when the radical nationalism of the late Julius Nyerere forced him and many of his colleagues out of their jobs. Now, old and poor, he is succored by a prosperous former student who gives him an apartment and hands him an old diary he discovered in one of his shops.

The book starts with the diary and grows into the narrative that Pius writes around it, based on research and interviews with descendants of three people who figure in it. Pius weaves in a reflection on his own lost life and a world that has passed away.

The diary of Alfred Corbin--eventually Sir Alfred and governor of Uganda--consists of stiff entries about his first post: the frontier settlement of Kikono, on what is now the Kenyan side of the border. Beneath the stiffness, he is a man of tolerance and compassion. He administers justice, tries to fight off the irascibility that comes with authority and isolation, and achieves a fondness (if no great understanding) for the inhabitants. Most are Indian Muslims.

The diary hints at Corbin’s attraction to his servant, Mariamu, the beautiful, high-strung niece of the community’s leader. When she marries Pipa, a young Indian trader, there is a wedding-night scandal: She is not a virgin. There is also a rumor--the diary records and denies it--that she and Corbin were lovers.

The war breaks out, Corbin is transferred and Kikono is disputed in desultory fashion between the British and the Germans. Pipa, who comes from the German side of the border, is forced to work as a British spy; the Germans conscript him as well. His no-man’s-land condition symbolizes the book’s sensitively depicted plight of East Africa’s Indians from that time to this. For Pipa it means beatings, arrests and death threats, and finally the mysterious murder of Mariamu, who had just given birth to a baby, Aku.

In the very sparsity of the diary’s detail, and in the account with which Pius supplements it, the book acquires a charge that is both alluring and troubling. The repressed Corbin, the half-wild Mariamu, the emotional Pipa become three points on a triangle; their vectors, half-hidden, hold a tense suggestiveness.

It is largely dispelled in the second half: Pipa’s later life as a shopkeeper in Dar es Salaam, bringing up Aku. He has acquired Corbin’s diary; unable to read, he imagines it must hold the secret that torments him. Is Aku, fair-skinned and gray-eyed, Corbin’s son?

Secret and torment notwithstanding, Pipa’s story declines into ordinary talkiness. So does that of Aku, who grows up to become an international financier. When Pius touches on his own life--an abortive love affair, a misunderstood friendship, the growing difficulties for Indians, his own sense of failure--his account is pallid. He is more alive pondering another’s story than inhabiting his own.