Kathryn and Sebastian are amoral step-siblings. Kathryn bets Sebastian a night with her that he can't bed Annette, the headmaster's daughter who is sworn to have no sex before marriage.
It's a little presumptuous to say that Cruel Intentions is "suggested" by Choderlos De Laclos' novel Les Liaisons Dangeureuses (as the opening credits tell us). However much this modernisation may want to distance itself from the French classic, it's as accurate a replication as you could hope to find, with cellphones and uplift bras replacing the corsetry and ugly smallpox deaths of the original. In fact, anybody who's seen the fabulous Dangerous Liaisons will be on familiar territory; the similarities, from character names to Phillippe's failed attempt to out-smooth Liaisons' John Malkovich, stand out a mile.
Gellar and Phillippe are wealthy New York step-siblings Kathryn and Sebastian; the former given to snorting coke out of a modified crucifix and shagging her way around the Upper East Side, the latter just given to shagging his way around the Upper East Side. In a bet to settle their lust for each other, however, they make a wager, involving virginal new headmaster's daughter Annette (Witherspoon). If Sebastian fails to pop her closely-guarded cherry before the start of the new term, Kathryn gets his vintage Jaguar. If, however, he succeeds, he gets Kathryn for the night. Cue: saucy shenanigans and subplots galore (mainly involving innocent pawn Cecile - a wildly mugging Blair), before Sebastian, deciding he quite fancies the hymeneally-blessed Annette, develops a moral centre.
With its parade of double entendres (coming across as a kind of Carry On Teens), hysterical adults, stupendously OTT performances and preposterous climactic "tragedy", this is the kind of movie which purists will dismiss as a mockery of the original.
Leaving aside the classy roots it has so shamelessly mangled, however, this is a lot of fun; Gellar does well, pouting and preening and throwing hissy fits all over the shop, as does Witherspoon, whose character seems remarkably eager to bed Phillippe given her strict stance on virginity (the woman has, clearly, been saving herself for Ryan's privates). And if Phillippe's acting extends only as far as an ability to convincingly put on his shades, and if the plot takes some swallowing, it doesn't stop this from being glossily enjoyable nonsense, the sort which will happily entertain for an hour-and-a-half without troubling the old grey matter too much.
Not quite as clever as it thinks it is, but still oozing more dark wit than most teen movies can dream of.