We start off introduced to the misanthropic and lovesick Alceste, who's got a thing for Célimène. She's is a lying liar who lies, and uses honestly as an excuse for being a jerk. Obviously, they'd be perfect together.
Or not. It turns out that a bunch of guys like Célimène, and everyone thinks that he is the one that she loves. But who is it really? Is it Alceste? Oronte? Clitandre? Acaste? Is it none of them? Are they all fools? We're not sure, and we don't even know very much about this Célimène chick except that she is a flirt.
Arsinoé shows Alceste a letter that Célimène wrote to Oronte and he flips out. The other guys realize that they are not the only ones seeking Célimène's affections and they decide to duke it out. We also learn a bit more about Célimène's reputation from Mrs. Arsinoé so we're pretty sure that Célimène loves none of these guys,
Well shnap. It wasn't surprising but we all know the truth now. Célimène is a trollop, a harlot, a strumpet, a tart. In other words, she is a player, and everyone is hating not just her game, but her.
In a dramatic scene involving some waving about of damning evidence, the truth is revealed. All the relationships in the play change. Célimène goes from being top dog to the bottom of the pack, and Philinte and Éliante go from being unrequited lovers to the only sane pairing in the play. Once everyone has said their piece, the play is not-quite-so-happily over.