"QUID PRO QUO" BY VICKI GRANT; ORCA, PAPER, $16.95

"Quid pro quo." It's Latin for "what for what," and in legal terminology means an even exchange. In the case of Canadian writer Vicki Grant's hilarious novel, the exchange is more than fair: Give this book a few hours, and what you'll get is a clever plot twist or two, a lot of laughs and a new favorite narrator.

Cyril MacIntyre is an eighth-grade snarkmeister with a whip-smart sense of humor — necessary, he says, for getting the girls' attention when you're built like Mr. Puniverse. Girls and his less-than-manly physique are concerns of Cyril's, but his preoccupation is with his chain-smoking, hotheaded mom, whom he just calls Andy. Andy, it seems, has a knack for getting herself into a jam.

For starters, Cyril is 14, and Andy is 29. ("Do the math," as Cyril instructs.) As a teen, Andy dropped out of school, did drugs, and was living on the streets when she got pregnant. Eventually, she pulled her act together enough to get into law school, but with no money for a baby sitter, had to drag little Cyril along to class. Some nights, he even stayed up late grilling Andy on client-solicitor privilege and zoning bylaws, while she smoked like a fiend. Kind of boring, but not a waste: Otherwise, "I wouldn't have known what I needed to know to save my mother's life."

Ever the rebel, Andy takes a position at a tiny law firm specializing in helping poor people and immigrants. She has no interest in joining her fellow law school grads at the fancy firms on the Halifax waterfront, where they will "see how much money they can squeeze out of their sleazy clients." When it comes to social justice, this is as polite as Andy gets; most of her other sentences have to be bleeped out by Cyril. (In a charming bit of realism, Andy eats at McDonald's every night, but won't let Cyril wear clothes bearing corporate logos.)

Cheap dinners aside, things are going well for Andy and Cyril. Then one night a tough-looking dude shows up at their apartment demanding to see Andy. Cyril gathers that Byron — with his "armpitty little beard" and lots of tattoos — is a refugee from Andy's less-than-squeaky-clean past. He's no charm-school graduate, either. ("Lord liftin'!" he tells poor, insulted Cyril. "You're some puny for grade eight!") The guy has some kind of hold over Andy, and she lets him stay at their place. That is, until Byron is implicated in the arson of a local historic building. That's when he disappears — and Andy is nowhere to be found, either.

With his mom gone, Cyril has to figure out what's going on, using partly remembered pieces of information from law school and a loony undercover routine. (At one point, he dresses up in Andy's clothes and covers his face with bandages, telling the law librarian "she" has just had "massive plastic surgery.") As he struggles to make all the connections, the book reveals itself as a nifty mystery.

At first glance, "Quid Pro Quo" is a modest little book, which makes it an even more exciting find. Grant's keen wit has a gentle, youthful touch reminiscent of Nick Hornby's. In fact, the book crackles with action and the kind of pop-friendly realism and humor that, like Hornby's, would come to life on screen. So it's hardly surprising that Grant is an award-winning TV writer and producer. In her hands, Cyril and Andy have a touching mother-son relationship — though, since it's characterized by not enough money and plenty of yelling IN ALL CAPS, it's never corny. Andy's sense of justice wins out — but she curses and swears straight through to the end.