The word tragedy has been revised downward until it means any profound, pointless loss -- the valedictorian killed by a drunken driver. One of William Harrison's achievements in this sure-handed historical novel is to remind us that tragedy has a stricter meaning that centers on the interaction between chance and the abysses in human character. The protagonists of this proper tragedy are two British explorers of Africa, Richard Francis Burton and John Hanning Speke.

In the annals of exploration, few colleagues have been so mismatched. The mercurial Burton was a swarthy Irish upstart, a preternaturally gifted linguist, a fine writer, a self-assured leader who knew when to browbeat a man and when to butter him up, a bear for sex. The saturnine Speke was a dyslexic blond aristocrat who read and wrote with difficulty, a crack shot, a sexually repressed Victorian, a tormented bundle of self-doubt and ambition. Ambitiousness, in fact, may have been the only significant trait the men had in common.

Like the myths of Greek tragedy, the story told in "Burton and Speke" is well-known. In June of 1857 the explorers set out to discover the source of the White Nile. A year later Burton is generally debilitated and afflicted with an ulcerated tongue. Speke pushes on without him. Speke comes upon a great lake west of Mt. Kenya, concludes that this is the source and names it Victoria. But he can muster few supporting facts upon his return, and Burton is skeptical. While he stays behind to recuperate, Speke sails for England. The agreement is that Speke won't present his finding to the Royal Geographical Society until Burton, the expedition's leader, rejoins him.

Four hours after reaching London, Speke goes to see Sir Roderick Murchison, president of the Society. Not content to announce the discovery and claim it as his alone, Speke slanders Burton, implying that lassitude, rather than physical illness, kept him from sharing the burden of discovery.

Speke is lionized, the repatriated Burton all but forgotten. Though depressed, Burton is reluctant to cause a ruckus. But he writes convincing rebuttals of Speke's position. (Burton's candidate for the Nile's source is Lake Tanganyika, some 200 miles southwest of Victoria.) Speke leads another expedition -- sans Burton -- to confirm his intuition but again fails to bring back hard information.

Dr. David Livingstone, the beloved dean of African exploration, sides with Burton. Others join the attack, and Speke's kudos deflates. He feels compelled to answer Burton at one of those grand public debates the Victorians love so well, and the stage is set for the tragic climax (which I'll withhold so as not to be a spoiler).

So much is fact -- at least as reported in such standard works as Alan Moorehead's "The White Nile" and Fawn Brodie's biography of Burton, "The Devil Drives." But Speke's motivation has always been murky: Brodie wrote of him, "Of all the great explorers, none was more enigmatic and less given to self-revelation . . ." Harrison's treatment of this material has it that Speke was homosexual and strongly attracted to Burton. (The author may have uncovered new evidence to justify this surmise: one of his acknowledgements is to a collateral descendant of Speke.) Harrison's Speke abhors his sexuality -- he calls it his "curse" -- and limits his activities to lavender-light districts.

He also projects his preference onto Burton. Though one has the feeling that Burton tried every sexual combination at least once and he did write a military report on male brothels in India, the man was a relentless womanizer. Nonetheless, during the interview at the Royal Society, Sir Roderick mentions the infamous report and asks, "Tell me in confidence. What do you know of his tastes?"

"Burton is a dark, dark man," Speke replies. "Take that as you want to!"

This interpretation of Speke is plausible and poignant. It accounts for his reticence and explains his obsession with Burton -- even at the height of his triumph Speke's lectures were as much tirades against his former partner as re-creations of the great discovery. In his fantasies Speke is powerful enough to live an openly unorthodox life. In reality he is devastated by self-contempt and unable to face the man he has loved and betrayed.

Harrison's version of the Burton-Speke relationship also has an ironic intensity rarely found in contemporary fiction. As in classical tragedy, the reader is both disheartened by the characters' self-defeating actions and delivered from chaos by the fateful pattern they form. (There is even a temporal irony involved. Had Speke been born a hundred years later, he probably would have made peace with his sexuality, but there would have been no great blank spots left to chart.)

All that keeps "Burton and Speke" from being utterly first-rate is its pedestrian style. Harrison, a veteran novelist and screenwriter, seldom writes a colorful sentence, and to get a sense of Africa's riotous physicality you have to turn to someone like Moorehead or Burton himself. What you won't find in Burton, though, is appreciation of the ultimate irony. He and Livingstone were off-base about the Nile's source, and Speke was quite right.