Dozens of HarperCollins staff — sales, marketing, publicity, and legal — have, for months, kept a book almost entirely under the radar. The Most Dangerous Animal of All, by Gary L. Stewart (Amazon rank, as of 1:30 p.m. Monday: #140,113), has no cover art. Its subject matter has been kept out of the press. But the book, which will be published tomorrow, does have an intriguing plot summary that reads, in part:

An explosive and historic book of true crime and an emotionally powerful and revelatory memoir of a man whose ten-year search for his biological father leads to a chilling discovery: His father is one of the most notorious-and still at large-serial killers in America.

Not mentioned in the summary: Stewart, a vice-president at Delta Tech Service in Baton Rouge, alleges that his father was the Zodiac Killer, who is believed to have killed at least five people in Northern California, and famously sent letters and cryptograms to Bay Area newspapers.

He reached this conclusion after twelve years of research, Tina Andreadis, a publicist at HarperCollins, told me this afternoon.

Approximately fifteen months ago, B.G. Dilworth Agency brought a proposal to HarperCollins's Michael Signorelli (an editor who has since left for Henry Holt). It was acquired within a week or two, for an amount HarperCollins declined to disclose. "It was a standard acquisition process," another publicist told me, "except for the NDA." Stewart was paired with writer Susan Mustafa, a veteran of the true crime genre.

The book — 367 pages, including the index — was vetted by HarperCollins lawyers, including Fabio Bertoni, who is now general counsel at The New Yorker. "Our lawyers felt it was legally sound," said Andreadis.

I asked if HarperCollins had contact with the San Francisco Police Department, for verification purposes. No, and apparently for good reason. According to the book, Andreadis said, the San Francisco Police Department "knew more than they're willing to admit."

She didn't share many details of the book, but told me that Stewart's father had a criminal record in San Francisco ("forgeries, bad checks"), and there was a strong resemblance between his father's mug shot and the police sketch.

Apparently, the police sketch was a good one. Said Andreadis: "If you look at Gary's photo next to the sketch of the Zodiac next to his father's mug shot, you can see that there is very clearly more than just a passing resemblance. They look alike."

"He didn't want to believe," she said. "I don't think most people want to know that their father is a notorious serial killer."