Spenser, as his many fans know, is the tough but literate hero of the detective series created by former English professor Robert Parker. Spenser is Travis McGee, but smarter, at least as far as book-learning goes, carrying William Butler Yeats and Gerard Manly Hopkins around in his head and possessing the self-awareness necessary for genuine wit.

He even has the ability to be witty about sex, and he likes women who are similarly inclined, an attribute that makes him a breakthrough figure in detective fiction. In "Mortal Stakes," an early novel in the series, Susan Silverman puts Spenser down for his macho, superman ways by observing, "I've seen the big red S on your chest." "That ain't all you seen, sweet patooti," Spenser rejoins. "I know," Silverman deadpans, "but it's all I remember."

Spenser's home is Boston, and he is wonderful at busting chops alongside the Charles or rescuing Red Sox stars who are in trouble, but "The Widening Gyre," the 10th Spenser novel, is largely set in Washington. Our hero has come to the Potomac to help a politician in distress, and, oh, what a falling off there is. One suspects Spenser is in territory dangerously unfamiliar to him as soon as he mentions Georgetown's Reservoir Avenue, and as the plot unfolds, one is sure of it.

Hired to provide security for a Massachusetts congressman who has decided to run for the Senate, Spenser is soon up to his size 48 jacket in the most simple-minded Washington stereotypes. There is Meade Alexander, the conservative congressman for whom Spenser works. Because Alexander shares the views of the Moral Majority, he must, of course, wear polyester (a "three-piece suit of miraculous fiber") and talk like a robot in need of oiling. "Well, you are physically imposing," he says to Spenser at one point, "but there must be a savagery in you that doesn't show normally."

Alexander's 46-year-old wife, Ronni, smiles adoringly while her husband gives speeches and drinks too much afterward. But that's not the worst Ronni does, her husband confides to Spenser. He has received a videotape of Ronni with a college boy. The young man is wearing only sunglasses, and Ronni is wearing even less. Spenser's mission: to fix things, without ever letting Ronni know anything is awry.

Possibly Parker meant to add some depth to Alexander's character by having him refuse to let his wife know about the videotape. "I would support Satan to spare her," the candidate says. But his decision doesn't make any human sense. On the one hand, Ronni is such an unattractive character that Alexander's dedication to her is puzzling, and, on the other, if he really is so dedicated, shouldn't he want to find out what her problem is so it can be dealt with? Having a character act in such an inexplicably arbitrary fashion is one of the worst sins a mystery writer can commit, because it encourages the reader to supply a cynical account of what's happening: i.e., this novel is only on Page 41, and if Spenser got to question Ronni about the videotape, it probably would end by Page 51.

Spenser suspects from the beginning that the videotape has been produced at the behest of Alexander's opponent in the Senate race. He is a mob-connected congressman named Robert Browne who is trying to ensure his own election by threatening to release the tape to the press unless Alexander drops out--a line of thinking so naive one wonders if this guy isn't too dumb even for the mob.

In a world where it is possible to cite at least one politician who was elected after himself being tape recorded in bed, what makes Browne--or Spenser--think a tape of a wife will prove fatal? Besides, any candidate with even a minimal amount of savvy who came into possession of such material would suppress it, knowing how easily it could backfire. Anybody who would set out deliberately to produce such a tape needs some basic lessons in political reality. And so does anybody who would write a novel in which that is a key element of the plot.

Usually we don't demand anything more than a passing acquaintance with reality from writers of detective fiction, but Robert Parker has demonstrated such fresh and insightful thinking in the past that we hold him to higher standards. Having widened the gyre a little too far in this novel, he should take Spenser back to the center, back home to familiar surroundings.