Move over, Spenser. Make permanent room on the streets of greater Boston for another sleuth who’s big (six feet one), strong, and tough as nails but soft at the core. Carlotta Carlyle — former cop, part-time cabbie — was a refreshing novelty in her debut, A Trouble of Fools. She was a one-in-a-million character saddled with a five-and-dime plot in last year’s The Snake Tattoo. But now, in Coyote (Delacorte), her third full-length appearance, Linda Barnes’ Carlotta emerges as a serious contender.

Don’t be misled by the garish book jacket, Day-Glo fuchsia and comic-strip trendy, that someone at Delacorte has slapped onto Coyote. Carlotta’s new case . is distinctly unglamorous and grimly earthbound — beginning with the brief, disturbing visit to her office from an illegal immigrant named Manuela Estefan. The terrified woman, who speaks English no better than Carlotta speaks Spanish, desperately wants to recover her immigration ID, her ”green card.” Unfortunately, the card is in the hands of the Boston Police Department, because another woman calling herself Manuela Estefan was carrying the green card when she was brutally murdered a few weeks before. So Carlotta soon finds herself at odds with the homicide cops (including an old pal) and local Immigration and Naturalization Service agents, both of whom are investigating a series of killings of female illegal immigrants.

When Carlotta’s client becomes the latest victim, the guilt-driven gumshoe intensifies her search for a murderous ”coyote”: somebody who takes money from would-be immigrants, promises them safe passage and good ”papers,” but leads them instead into lives of exploitation and despair as illegal aliens.

An original idea? Not particularly. But it’s a somber, powerful one, and novelist Barnes shrewdly counterpoints the grimness with Carlotta’s zest for blues records, volleyball at the Y, and cruising around Boston neighborhoods in her cab. Furthermore, the almost documentary-like central story is layered with a more personal and distinctive tale: Carlotta’s long-standing connection, through the Big Sisters Association, to 10-year-old Paolina, who lives in a run-down Cambridge housing project with her ailing Colombian mother and four older brothers. Barnes constructs a satisfying, if unsurprising, link between Paolina’s growing pains and the grisly murder mystery. She also does a better job than Robert B. Parker when it comes to giving a hard-boiled detective a mile-wide sentimental streak. Carlotta’s devotion to Paolina may get a trifle sticky, but for the most part it’s understated, convincing, and blessedly free of the self-righteousness that afflicts Parker’s Spenser whenever he befriends the young and the helpless.

True, Coyote is far from perfect. The climax, a kidnap-hostage showdown in the Boston subways, sacrifices credibility for movie-minded melodrama. Carlotta’s relationship with a romantic INS agent owes too much to formula. And Carlotta’s narration, though still effectively lean and wry, seems a bit less brightly humorous than in Barnes’ previous books.

Never mind. A promising American detective has come into her own and joined the small but growing lineup (Sara Paretsky’s V.I. Warshawski, Sue Grafton’s Kinsey Millhone) of commanding, hard-boiled heroines. A-

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