The character Forrest Gump, invented by novelist Winston Groom and turned into a household name by Tom Hanks in the 1994 movie, has a lot in common with real-life character Terry Lenzner, a lawyer/private investigator who is a household name in Washington, D.C., political circles. The main difference is that unlike the movie character, Lenzner is blessed with a very high IQ.

Books by Washington insiders often promise a great deal, then fail to deliver. Lenzner delivers. His memoir, "The Investigator: Fifty Years of Uncovering the Truth," is loaded with details about his role investigating numerous scandals, starting with the shameful behavior of Richard Nixon that led to his departure from the White House.

Lenzner is candid about the heroes and villains he has encountered, and candid about himself. Yes, he has plenty to boast about, and he is not always above boasting. Mostly, however, Lenzner is self-effacing, sharing credit with mentors and colleagues, while admitting that he has sometimes been mistaken about the morality of investigative targets.

Lenzner made a difference initially as a young civil rights lawyer within the U.S. Justice Department. Growing up in New York City, he understood little about the Deep South and found himself shocked at the brutality visited upon blacks who attempted to vote and exercise other basic rights. When the brutality turned to murder, Lenz­ner learned that achieving justice would not come easily.

Lenzner received a different kind of schooling as assistant chief counsel to the Senate Watergate committee investigating Nixon and Nixon's henchmen. The portraits provided by Lenzner from his ringside seat help flesh out the gazillions of words already published about Watergate. A few heroes even emerge, especially Sen. Sam Ervin of North Carolina, who chaired the Watergate committee.

Eventually, Lenzner decided to strike out on his own, founding Investigative Group International, which has attracted fascinating, powerful clients worldwide. The wide-ranging memoir discloses Lenzner's role in investigating the death of England's Princess Diana, the allegedly corrupt administration of Venezuelan President Hugo Chavez, and the sometimes false allegations against Bill Clinton during his presidency.

Different readers will be most attracted to different case studies. My favorite, because of its rich detail: the 1990s investigation of the supposedly squeaky-clean United Way, run, it turns out, by honcho William Aramony as a personal fiefdom.

Steve Weinberg is a former Washington correspondent for newspapers and magazines who now writes and reviews books full time.