By John Darnton

Knopf. 309 pp. $24.95

Pity Charles Darwin. He sailed on the Beagle on the 27th of December, 1831, returning five years later with the germ of his "transmutation" theory. Shattered, he withdrew for life to Down House in Kent, fathering 10 children and suffering from anxiety. The problem? His discoveries could destroy both the British orthodoxy and his own comfortable position within society. As he wrote in his diary, "Once grant that species . . . pass into each other . . . & whole fabric totters & falls." Announcing such a belief, he confided to a friend, would be "like confessing a murder."

He might never have done so, except that Alfred Russel Wallace came to similar conclusions while collecting specimens on the Malay Archipelago and threatened to publish first. But in 1859 Darwin beat him to the post: "On the Origin of Species by Means of Natural Selection" seized the day. It might have made him an outcast. Instead, thanks to a campaign by his friends, he was lionized and lies buried in Westminster Abbey. But time has brought more questions. What took Darwin so long to publish? Why did he suffer bizarre nerve and stomach illnesses and resort to self-torturing remedies such as strapping ice packs on his spine and hanging chains around his neck for the rest of his life? Did the wrong man get the credit?

John Darnton thinks so. In his new novel, "The Darwin Conspiracy," he returns to the Beagle's grueling South American voyage, attributing to his fictional Darwin actions that, if true, would completely recast history. Darnton, a reporter and editor for the New York Times who won a Pulitzer Prize for his coverage of Poland under martial law, tells three tales here: the story of Darwin as a young explorer; the story of Lizzie, Darwin's daughter, told through her fictional journals and letters; and the present-day story of a pair of researchers named Hugh and Beth. They meet on the Galapagos and again in England, where they join forces to unearth the "truth" about the great man who is, coincidentally, Beth's great-great-great-great grandfather.

If there is a set of requirements for the idea-driven popular novel that serves up fast-paced history and questions of consequence, "The Darwin Conspiracy" has them all: The academic sleuths come from two directions and join forces. They are attractive and young. They find hidden letters, secret diaries, spurned relations. A romance develops. They chase clues from hither to yon. Their emotional lives parallel the historical lives as the chase speeds up, and it all works out in a last-minute discovery. Think A.S. Byatt's "Possession," and its many (often pale) imitations -- most recently, of course, "The Da Vinci Code."

Here, the devices strain to keep up with the ideas. Lizzie is far too adept at finding her father's secrets. Captain FitzRoy and Richard Matthews, a young missionary, have conveniently left descendants with attics. There are so many halfhearted escapades to find documents to explain the next bit of the puzzle that even the author seems to tire of the plot. Scene after scene is presented only as an interview; almost all the key dramatic episodes are related from the wings. I kept wanting to say, "Please don't tell this through another letter, Mr. Novelist. Take me there -- to that bubbling volcano, to that massacre by natives. You're allowed: It's fiction."

But Darnton scrupulously sticks to his sources, imaginary though they are. And so the characters remain at a distance. Darwin is ever unsympathetic. The painstaking, scrupulous research scientist who followed through on his theory, offering proof, is not here. Only Lizzie has promise; she is easily her father's match, as she "allows him to win" at backgammon and watches him stammering and lumbering around with ice packs on his spine. But she's soon packed off to a Swiss sanitarium for knowing too much.

Fortunately, the novel comes to life in the idyllic scenes of the younger Darwin and his sometime rival Robert McCormick scouring the South American shores. Imagination trumps research when Darnton draws the "savages" of Tierra del Fuego, and he shows the incomprehension of the English surveyors who carry their righteousness around the world. He's got the smugness right. As Darwin remarks, "Nature smiles upon those She favors." In the novel's world, it is society's favored -- such as wealthy, well-connected Charles Darwin -- who survive, not the fittest.

Darwin got the credit for evolution because he was a gentleman with powerful friends. No surprises there. But when Darnton takes literally a murder that Darwin did not confess to, it's a bit much. And hackneyed descriptions reminiscent of historical romance ("sin-encrusted lower depths") also mar this interesting speculative history. Nonetheless, when the seasick 22-year-old cleric sailed on the Beagle, events began that changed the way we see the world.

Even with its sometimes overheated, sometimes tired writing, "The Darwin Conspiracy" is worth reading for its reexamination of this crucial -- and still controversial -- moment in time.