"Flu: The Story of the Great Influenza Pandemic of 1918...

"Flu: The Story of the Great Influenza Pandemic of 1918 and the Search for the Virus That Caused It," by Gina Kolata. Farrar, Strauss and Giroux. 246 pages. $24.

Why did 20 million -- or maybe 100 million -- people die of the flu in 1918?

We need to know. Should a similar pandemic strike now, 1.5 million Americans would die.

Alas, "Flu" doesn't -- can't -- tell us why the 1918 flu was so lethal. We don't know, not yet, even if scientists have come tantalizingly close in the last year to cracking the genetic code of that deadly virus. We know enough to fill a book, but not enough to complete a satisfying story.

Which is a shame, because "Flu" is meticulously researched and clearly written by Gina Kolata, a science reporter for the New York Times.

The early chapters, on the plague and how it killed, are terse and gripping. But then the story must go to the attempts to understand the 1918 flu, the first step to vanquishing any hellish return. Kolata has a clear path, but wanders off mid-book.

If you can get past the center section, the book picks up in its descriptions of the race to decode the 1918 flu.