Q: Who's the cruelest, most smugly self-righteous, and least believable assassin to appear this season? A: Tessa, the heroine/narrator of Weyer's far-fetched and forbiddingly violent first novel. According to the publisher, Weyer is "an adventure training instructor for British forces posted in Belize"; her survival know-how is on peacock display in the rigorously authentic climbing and spelunking scenes that pepper her brief (160-page) narrative. What isn't evident is much subtlety, beginning with Tessa's job: assassin for "The Watchdog Organization," the clandestine arm of--if you can believe it--the World Council for Human Rights. When human-rights violators (mostly left-wing here) get too annoying, in steps Tessa with her lethal-weapon hands, a bomb, or the rifle that she calls "Beauty." Why does she kill? Maybe because commies raped and tortured her mom before her very eyes. This and other background facts we learn during stiff patches of dialogue--dialogue that also details Tessa's current mission: to travel to Belize to waste Ronald Jedson, a pesky KGB agent. After some kinky sex with her knife-throwing Afghani lover, Blade, Tessa flies to Belize, where she stays with her half-brother, Ken. After zapping Jedson (with a bit of sideline torture that includes cutting off someone's eyelid), she's about to leave when she learns that Ken's been kidnapped. By whom? By someone who forces her to strip naked and watch as Ken must saw off one of her fingers with a dull knife and then. . . A lemon thriller: astrigent action with a sour aftertaste.