Orgon, the head of a prosperous family, has taken in and been taken in by Tartuffe, a man who purports to be holy, but is really a fraud. Orgon and his mother are the only ones to have fallen under the trickster's spell – the rest of Orgon's relatives, including his wife and brother-in-law, see right through Tartuffe.
The stage is set in Act 1, Scene 1, during a long interaction between Madame Pernelle and the rest of the characters – excluding Orgon and Tartuffe, of course. It's all exposition, really, but it gets things up and going quickly.
Orgon tells his daughter Mariane that she will be marrying Tartuffe instead of Valère, her longtime fiancé.
Although pretty much all the characters hate Tartuffe already, this development puts them into crisis mode. Dorine, Mariane's servant is especially vocal when expressing her displeasure. Tartuffe won't budge, however.
Tartuffe attempts to seduce Orgon's wife, Elmire. Elmire shuts him down, then makes a deal with him: if he'll convince Orgon to let Mariane marry Valère, she won't tell Orgon about the incident. When Damis decides to tell Orgon what's happened, Orgon refuses to believe him – and disinherits him instead. Tartuffe is made the sole heir to Orgon's fortune.
Events unfold very quickly and things get complicated – very complicated – just like that.
Elmire decides that Orgon needs to be shown the truth as quickly as possible. She makes Orgon hide under a table while she "seduces" Tartuffe. Orgon is horrified by what he sees and confronts Tartuffe.
This is where everything changes; Orgon, finally sees the light.
Tartuffe vows to get back at Orgon. He leaves quickly. Orgon realizes he's in quite a pickle. He's already signed over all his possessions to Tartuffe, and, to top it all off, the swindler has run off with some incriminating documents.
At this point, we know things aren't going very well, but we don't know how much damage Tartuffe is going to do. He's got the ball in his court, so to speak.
We hear that the documents Tartuffe has gotten off with could land Orgon in jail. Tartuffe's representative, Monsieur Loyal, shows up and tells Orgon that he's being evicted and will have to leave the house by the next morning. Valère rides in and convinces Orgon to flee the country immediately; he's made preparations for his flight.
Things come to a head here. It looks like Tartuffe has really nailed Orgon, and the only option Orgon has left is to flee the country.
Tartuffe shows up, policeman in tow, to arrest Orgon. He's shown the damning documents to the King. The policeman arrests Tartuffe instead, and explains that the wise King could see through Tartuffe's ruse instantly. Orgon is given back his property and absolved of any wrongdoing, Tartuffe is taken away, and Mariane and Valère are slated to be married.
It's a picture perfect conclusion, complete with a marriage. The good guys win, the bad guys lose, and all is right in the fair kingdom of France.