To enjoy mystery fiction, it helps to have a strong, interesting protagonist -- not necessarily likable (although that helps). If you're going to invest a few hours in somebody's adventures, it's easier if you can relate to them, admire them or be sufficiently involved to care what happens next.

"Merciless" by Lori Armstrong (Simon & Schuster, $15, 330 pages). Mercy Gunderson is no longer in the army, but she still takes no prisoners. The rural South Dakota-based woman with deadly aim is now a newbie FBI agent, and her first case involves the torture and death of a young Native American woman on the reservation.

There are jurisdictional issues involving the tribal police and Mason Dawson, the local sheriff who happens to be Mercy's live-in partner. Then there's her supervising agent, who seems to have his own agenda. When Mason's 11-year-old son arrives to live with them, commitment-phobe Mercy struggles to adjust.

But most of the story revolves around the case, which is neither the first nor the last involving an unsolved crime on the reservation. The story is gritty, terrifying and overflowing with life (and death). It makes compelling reading from start to finish.

"Unnatural Habits" by Kerry Greenwood (Poisoned Pen Press, $24.95, 304 pages). The unstoppable Phryne Fisher continues to use a combination of smarts, guts and charm to solve dreadful crimes in 1929 Melbourne, Australia.

Phryne's newest case starts with Polly, an eager young woman trying to become a reporter, who disappears while in a dangerous part of the city. Phyrne soon discovers that other girls have disappeared, some of them pregnant, and some very young and blond.

She gets help from a gay men's club, a devoted policeman, her married Chinese lover and her own ill-assorted but eager household.

I was bothered by Polly's admission that she stole the important story her irritable boss was working on, and Phryne tells the boss to get over it! In real life, no one in the business would ever trust Polly again -- and not because of her gender.

In other words, you can't believe a word of this story, but reading it is still fun.

"A Plague of Lies" by Judith Rock (Penguin, $15, 352 pages). Charles du Luc, an instructor at a Jesuit school in 17th-century Paris, finds himself sent to Versailles to care for an ailing teacher as part of a delegation presenting a gift to Louis XIV's second wife.

At this time, the king is all powerful, and there is a constant push and pull between the secular and religious authorities. Charles, who just wants to go back to his normal life, gets caught in the undertow when a courtier dies, perhaps from poison. In the course of his reluctant investigation he gets to know Lulu, one of the king's daughters who clearly never got the manual about how princesses are supposed to behave.

All the books in this series are very well researched, but never didactic. Rock pulls you into this alien world, which is fascinating, terrifying and surprising all at the same time. And Charles, who turned to the Jesuits after life as a soldier, is well worth getting to know.

"Unleavened Dead" by Ilene Schneider (Oak Tree Press, $16.95, 288 pages). Rabbi Aviva Cohen is still running a little synagogue in New Jersey and sticking her nose into every possible crime in the neighborhood.

This time there are two: the hit-and-run death of a psychologist, with the prime suspect being the recently fired girlfriend of Aviva's niece; and the death by carbon monoxide poisoning of a couple from the congregation.

The couple had wanted Aviva to perform their daughter's wedding ceremony in Oregon; she had refused because it was an interfaith marriage.

What works quite well here is the depiction of small-synagogue life, the rabbi's many duties and the interactions of the members. Plus, there are lots of delicious goodies being served all the time.

What doesn't work is more complicated to explain. I sense we're supposed to like Aviva, but her extreme nosiness is off-putting. It made me want to pull down the shades so she couldn't tell I was at home.

She's also a gossip, a serious sin in Judaism. She acknowledges that she shouldn't be, but then justifies telling anyway. This does not make her more likable or admirable.

And I wish Schneider had had a little more editing, someone to remind her that Aviva does not have to repeat all of her suspicions to each new person she talks to.

By the time I got to the rather far-fetched solution, even the dessert plates had lost their allure.

Roberta Alexander is a member of the National Book Critics Circle. Her "It's a Mystery" column is published here monthly. Contact her at ralex711@yahoo.com.