I'm supposed to be reviewing John Grisham's sequel to "The Firm," called "The Exchange," in this space. Instead I'm going to write about a thriller that's actually good.

"The Exchange" is a baffling book. Mitch McDeere (played by Tom Cruise in the "Firm" movie) is back, 15 years after those events, but he never steps foot in a courtroom in Grisham's 49th novel, which is not even a legal thriller.

Instead, it's an international kidnapping melodrama, with a victim we don't care about and a bizarre opening 40 pages that have nothing to do with anything that comes after — a bait-and-switch that reads as if Grisham got bored with the legal thriller he started (a death row case) and decided to shift gears.

Nostalgia for "The Firm" will lead tons of readers — like me — to pick up the sequel but, instead, I'd recommend another newish thriller about a guy who, like McDeere, treads on both sides of the law, Dwyer Murphy's "The Stolen Coast."

It's a contemporary update of the hard-boiled detective novels of Raymond Chandler and Dashiell Hammett. The narrator is Jack Betancourt, although we don't learn his name until the book is nearly over — one of many devices Dwyer uses to keep us off-balance as Jack and an ex named Elena plan to swipe some raw diamonds owned by a wealthy resident of their seedy Massachusetts village.

The fun of "Stolen Coast" is in how Dwyer messes around with what he knows we know about this sort of novel. There are sly allusions to the noir-ish movie "Body Heat" — including a cameo appearance by its late star, actor William Hurt — and Dywer gets lots of mileage out of the idea of Elena as a femme fatale. Jack knows she's using him; he's not an idiot. But he isn't sure how much she's using him and whether she's being straight with him when she invites him into the jewelry heist plot.

"Stolen Coast" is more deliberate than most thrillers because Dwyer is less interested in plot than character dynamics. Betancourt has plenty of zesty, cynical observations — "I wanted very badly to rob the man. It seemed like he was crying out for it to be done," he comments on the eve of the heist. But, unlike most of his predecessors, he has a conscience. In fact, he spends much of the book sorting out what it would mean to do the right thing in a world where so many profit from doing wrong.

In those '30s and '40s novels, the hero may have been crooked, but he seemed to be searching for a code of honor that made sense to him. That's what Betancourt is doing, too. The ending of "Stolen Coasts" leaves us with some questions about what might come next and its hero with the knowledge that there's more good in him than he realized.

The Exchange
By: John Grisham.
Publisher: Doubleday, 352 pages, $29.95.

The Stolen Coast
By: Dwyer Murphy.
Publisher: Viking, 288 pages, $28.