In the 1970s, after Watergate became a part of the American vocabulary, the investigative reporter joined the cowboy, the pirate, the private eye and the spy in the front lines of our folk mythology. Journalism schools began pumping out candidates for this mythic role at an alarming rate, and schoolboys who had once aspired to be firemen or astronauts began to carry notebooks and to look for possible malfeasance in the administration of their kindergarten milk and cookie funds.

John Weisman, a versatile journalist who writes about the field with first-hand knowledge, may help to reduce the popularity of this career choice. Just as nobody would aspire to be John le Carre's antihero George Smiley, nobody who reads "Evidence" is likely to want to be Jack Fowler, an investigative reporter who is murdered, or Robert Mandel, a friend and fellow reporter who has to write Fowler's story. After reading "Evidence," you might conclude that investigative reporters have a role in society, but you wouldn't want your sister to attempt a meaningful relationship with one -- or your brother or your juvenile cousin, for they come in a variety of sexes.

Even their social value is left in some doubt. The investigative reporters in Weisman's novel are something like poets and something like cops. They resemble poets not only because they become obsessed with their work at the risk of their personal lives and their sanity, but because they recall something that W. H. Auden once said: "I do not think that writing poems will change anything."

Mandel sees the same problem, but he relates it more clearly to the work of the police: "We can no more change things than the cops can. Yet we, like they, hit the streets everyday. Looking for something to write about. Something awry. A new victim, a different story, a fresh snitch. Something with a twist . . . Seldom do we save a life, force a change. We simply watch as 'they' do damage to each other. We keep the score, tote the victims in the obituary column."

A good story on drug traffic in Detroit (which is Mandel's beat) does not reduce the traffic. It may send someone to jail or close down a particular operation, but the vacuum is filled immediately, and the only practical result is that a new corrupt official begins to get the bribes, a dealer moves from one street to another. The story becomes, like a poem, an end in itself -- a life-involving end. "Would I kill for a story?" Mandel asks himself in a moment of truth. "I would give it serious consideration, if the story were good enough," he concludes.

But that is an extreme case. Most of the time, he is like a warden in a wildlife preserve, watching the animals kill one another from the safety of his Land Rover. His life is protected and hedged in by rules: don't make friends with your sources or write about friends; avoid conflicts of interest; look as if you belong on the scene, but don't get involved, don't feel anything on the job except the job; don't let your subjects or sources know where you live; get everything you can on tape; maintain strong defense perimeters and (rule No. 1, because it is an editor's rule as well as a reporter's): get the story before your competition does.

In narcotics reporting, the rules can be a matter of life and death, but even when the stakes are lower they are important. Without rigid rules, Mandel feels, "I would eventually become the same as the victims I wrote about. Without rules I would be manipulated; I would just let things happen instead of making them happen."

Before coming to Detroit, Mandel lived in Los Angeles with a television writer named Nancy, who "said I was emotionally dead. She said that in the six years we had lived together she had watched my emotions petrify into stone. She called me cold, calculating, and manipulative. Maybe she was right. Probably she was." Nancy tended to blame it on his rules, but she was probably mistaken. The rules may have been a symptom of the problem that caused the death of feeling, but the problem was the work he did, the people with whom he associated: "As my stories got better, my personal life got worse. It couldn't be helped."

Jack Fowler's problem was that he thought he could break the rules; he was a bisexual who wanted to get out of court reporting into investigative reporting by doing a story on chicken-hawking, the homosexual prostitution of young boys. Then be began to sympathize with the victims he met, he let his address be known, and he was dead. Mandel dropped his drug beat for a while to investigate Fowler's death, and that too was a mistake; Fowler was a friend, and you don't write about friends.

Weisman's account of how Mandel gradually unwinds the story of Fowler's death takes the reader through some very rough scenery -- not only in the haunts of drug-pushers and pimps, but in the offices of a prosecuting attorney and an editor. The scenes are somewhat more vivid than those in the life of an average reporter, and Mandel's tape-recording gadgetry is more elaborate than what you will see in most newsrooms -- probably in most CIA establishments. Mandel is clearly an extreme case, but through him Weisman takes an intelligent, penetrating look at what it is like to be an investigative reporter -- not only the techniques, but the feelings (or non-feelings) and the ethnical problems connected with the work.