Cruel Intentions, writer-director Roger Kumble's debut film, is a surprisingly faithful retelling of Choderlos de Laclos' novel Les Liaisons Dangereuses, famously adapted into the film Dangerous Liaisons. Set in modern-day New York, the new version tells the story of a malevolent high-school lothario (Ryan Phillippe) whose treachery is more than matched by that of his promiscuous, cocaine-addled stepsister (Sarah Michelle Gellar). The two make a wager to determine whether Phillippe can seduce the chaste daughter (Reese Witherspoon) of their school's new headmaster, a bet that eventually forces Phillippe to re-examine his hedonistic existence. For its first 45 minutes or so, Cruel Intentions works as a sort of glossy, enthusiastically mean B-movie along the lines of Wild Things, another self-consciously transgressive film that fell apart toward its second half. Kumble began his career writing lowbrow comedies (National Lampoon's Senior Trip, Kingpin, Dumb And Dumber), so it's not surprising that the first half of Cruel Intentions aims low but consistently hits its targets. Like its protagonists, however, the movie is good at being bad, but more than a bit confused when called upon to repent for its sins and follow the straight-and-narrow path. When Phillippe develops feelings for Witherspoon, it does fatal damage to Cruel Intentions' trashy, dark-comic sensibility. Part of the problem comes from the limited range of its two leads: Phillippe is fine when he's doing his menacingly pretty teenage-fop routine, but seems lost when called upon to exude anything resembling emotional complexity. As for Gellar, well, it remains to be seen whether she can convincingly play anything but a vampire-slaying high-school vixen. Cruel Intentions is smarter and funnier than anything in the recent cycle of high-school sex comedies (Varsity Blues, She's All That, Can't Hardly Wait), but it's little more than a wildly uneven, sporadically enjoyable guilty pleasure.