Two Metro reporters at the Washington Post, both in their late 20s — one a dogged investigator who writes badly, the other rather a flake who writes well — team up to take down a president of America. The plot for a bad movie? No, actually the scenario for a rather good one, “All the President’s Men,” and, improbably, a true story — although to give the whole credit for Watergate to Messrs. Woodward and Bernstein is (as Huck Finn would say) a stretcher.

Why were Messrs. Woodward and Bernstein so successful? They were ambitious, single, and single-minded. While many veteran journalists kept saying Richard Nixon would not be so stupid as to tie himself directly to the burglary at the Democratic party’s Watergate Hotel headquarters, “Woodstein,” as the duo was dubbed, simply kept asking questions and going after sources.

But this is not the whole story. As Alicia C. Shepard recounts in her absorbing biography, “Woodward and Bernstein” (Wiley, 304 pages, $24.95), Carl Bernstein had grown up in Washington, D.C., and worked in newsrooms since the age of 16. He had a nose for news. Bob Woodward, growing up as a conservative Midwesterner, seemed constitutionally curious about the secrets people and institutions zealously guarded. He believed in openness. He had no agenda; he simply wanted to know.

But this is not the whole story.”Woodstein” needed and received the full backing of their newspaper. Even when other major papers like the New York Times did not accord Watergate much space, the young reporters got the go-ahead from their immediate supervisors as well as from the newspaper’s executive editor, Ben Bradlee, and its owner at the time, Katharine Graham. Graham risked Nixon’s wrath — there was talk in the White House about revoking the Post’s television licenses — and the contempt of other newspaper owners who doubted her judgment in allowing Mr. Bradlee to back Woodstein.

But this is not the whole story. Ms. Shepard believes the primary reason for Woodstein’s success was their status as outsiders. They were beholden to no one. They had no reputations to lose, really, and they could not be co-opted by politicians. They bonded together as outsiders — a development Ms. Shepard acknowledges but does not fully explore.

“There are special things only the two of us understand, from the work we did together to the way each of us looks at journalism,” Mr. Bernstein told Ms. Shepard. Boy, did that ring a bell for me. Having written several unauthorized biographies, I know that the reporter often becomes the target, not just the subject of the investigation. Family members, friends, and the press (reviewers) all pile on to question the motives of a journalist like Bob Woodward, who simply wants to know. When Mr. Woodward published his biography of John Belushi, Bill Murray, Belushi’s “Saturday Night Live” colleague, said publicly that Mr. Woodward deserved to be put to death.

But this is not the whole story. Mr. Woodward developed a crucial source that became the celebrated “Deep Throat.” Neither Messrs. Woodward nor Bernstein ever claimed that Deep Throat had the key to Watergate. Instead, he served as a sounding board for Mr. Woodward, pointing the reporter in the right direction by asking provocative questions. Mr. Woodward never voluntarily disclosed the identity of his source, and then did so only reluctantly after Mark Felt’s family decided that what they deemed his heroic role should be acknowledged before he died. Why Mr. Woodward balked at full disclosure is a story in itself.

Mr. Woodward had always said he would not unveil Deep Throat’s identity until the source died. Felt no longer was mentally competent at the time his family through its lawyer divulged Felt’s role in history, but Mr. Woodward still felt bound by his promise. Only when his own newspaper pointed out that it had to cover this news story did Mr. Woodward confirm the family’s account and then publish his own version of his relationship with Felt.

Mr. Woodward’s use of anonymous sources has been his bête noir. His fellow journalists have repeatedly questioned his ethics and his veracity. How are they to believe what he has reported about the inside deliberations of the Supreme Court, the CIA, or the Bush and Clinton White Houses, when they cannot check his evidence? Especially troubling to his critics has been his use of omniscient narration. How can he know what his subjects are thinking?

Much of this criticism, in my view, is misguided. Omniscience, in Mr. Woodward’s books, is a literary technique, not a claim to an all-knowing, definitive account of history. Here is what happens: A source, X,says “I felt like resigning when I discovered that Nixon had done such and such.”To Mr. Woodward it becomes, “X felt.” The drama and immediacy are enhanced. He has not made anything up.

Of course, there is a downside to using anonymous sources, since who said what can be as important as what was said. But Mr. Woodward has never offered his model of investigative journalism as one the whole profession should emulate. Mr. Woodward has yet to be caught out in a significant error. More importantly, though, there is nothing stopping other reporters from doing their own work to corroborate or refute Mr. Woodward.

Mr. Woodward has been so much more productive than Mr. Bernstein that it seems inevitable that his work should dominate a dual biography. It is to Ms. Shepard’s credit, however, that interest in Mr. Bernstein never flags. She treats his marital and professional failures sympathetically without excusing his bad behavior or injudicious career moves. His move to ABC television was a disaster, and the few books Mr. Bernstein has written have received mixed reviews and made little impact. Certainly, he has suffered far more than Mr. Woodward from the “shadow of Watergate.” Nevertheless, Mr. Bernstein remains an appealing figure, owing to his lack of self-pity and his enduring relationship with Mr. Woodward, despite the ups and downs of their friendship.

Ms. Shepard has benefited from the huge archive Woodstein sold to the University of Texas. Both men were available for interviews, and she diligently canvassed opinions from friends, former friends, and associates. The result is a richly detailed book that does justice to both history and biography — an impressive achievement in a well-wrought narrative of fewer than 300 pages.

crollyson@nysun.com