Dennis Lehane's last novel from 2017, the psychological thriller "Since We Fell," was his first to unfold through a female protagonist's perspective. Rachel Childs was a formidable heroine whose concealed traits and surprise impulses were revealed with each narrative twist and turn. Lehane's latest novel, "Small Mercies," is fronted by another strong woman. Single mother Mary Pat Fennessy is described by a character as "broken but unbreakable." She is also unstoppable as she embarks on a mission that is both a search for answers and a quest for revenge.

Lehane's high-octane drama plays out against a backdrop of historical events. It is the torrid summer of 1974 and the eve of Boston's controversial desegregation of public high schools. In South Boston, Mary Pat's white, working-class, Irish-American home turf, mob chief Marty Butler — "Southie's protector" — has organized anti-busing protests. Mary Pat finds herself with a far more pressing concern when her 17-year-old daughter Jules fails to come home one night. The following day, Mary Pat shows up for work at Meadow Lane old folks' home and discovers that her Black colleague's son, Auggie Williamson, was found dead on the track of a subway station early that morning.

Jules still doesn't appear so Mary Pat makes her own inquiries throughout the neighborhood. She shows her daughter's knuckleheaded boyfriend who's boss and dredges up the past with an unwelcome visit to her ex-husband. She learns that Jules has been hanging around with George Dunbar, an "untouchable merchant of poison" whose drugs killed her son, Noah. As if that news wasn't bad enough, she is hit by the bombshell that Jules has been the mistress of one of Butler's henchmen.

When Detective Bobby Coyne arrives on the scene chasing a lead that links Jules' disappearance to Auggie's death, Mary Pat is buoyed by the breakthrough. But then Butler informs her that her investigations are creating too much noise and tries to buy her silence. Fearing the worst but refusing to back down, Mary Pat, "built for battle," becomes a one-woman army.

"Small Mercies" is vintage Lehane. The dialogue is punchy, the action gritty and the mystery intriguing. Lehane's prose is deliciously raw: Jules is waiting on a broken heart "the way miners wait on a black lung"; Mary Pat breaks a nose with her fist and "it sounds like a cue ball shattering a tight rack." There is expertly cranked-up tension, with both the social unrest ("this city is about to go boom") and Mary Pat's decision to cross "a border between worlds" and take on Butler and his crew.

The book's main highlight, though, is its central character. Mary Pat, who "looks like she came off a conveyor belt for tough Irish broads," is a true force of nature and one of Lehane's most memorable creations. Despite, or perhaps because of her flaws, we champion her all the way through this electrifying tale about race relations, retribution and power.

Malcolm Forbes has written for the Times Literary Supplement, the Economist and the Wall Street Journal. He lives in Edinburgh, Scotland.

Small Mercies

By: Dennis Lehane.

Publisher: Harper, 320 pages, $30.