Irascible gumshoe Gary Aldrich was in the news again this week, when New Yorker writer Jane Mayer quoted the former FBI agent and bestselling author as saying that some of the allegations he made about President Clinton in Unlimited Access were "hypothetical" and "not quite solid."

Aldrich denied it and threatened to sue -- probably ill-advisedly, since Aldrich himself told Newsweek last year that many of his stories were " only allegations that needed to be further investigated."

The Mayer-Aldrich spat presented a problem of allegiance for conservative investigative journalist David Brock. Last summer, Aldrich revealed Brock as the source for his most controversial "allegation": that President Clinton had sneaked out of the White House for a tryst, hidden in the back of a station wagon. Brock promptly denounced Aldrich, countering that he had merely asked Aldrich about the story during an interview.

The result was an exchange of heated accusations of mendacity and some bizarre hate-mail from the pen of Aldrich. So Brock would clearly --

But wait: Mayer co-wrote with onetime Wall Street Journal colleague Jill Abramson) one of the most negative (and in Brock's view, dishonest and self-interested) reviews of his account of the Hill-Thomas affair, The Real Anita Hill. When Mayer and Abramson wrote their own Hill-Thomas book, Strange Justice, Brock replied in the American Spectator with a devastating catalogue of factual errors that stretched to 22,000 words.

So whom to believe when liars call liars liars?

"Regnery [Aldrich's publisher] and the conservative media outlets that embraced the book," Brock told the Washington Post, "are going to have to give the public an explanation or an apology."

It's Mayer by a (held) nose.