Cléante attempts to convince Madame Pernelle that Tartuffe is a hypocrite. He fails.
Cléante greets Orgon, who has just returned from the country. He is blown off; Orgon is more interested in hearing about Tartuffe.
Cléante confronts Orgon and tells him he's acting like an idiot. He listens as Orgon describes what a wonderful dude Tartuffe is, but he doesn't believe it.
He chews Orgon out, calling him a dunce in a dozen different ways and teaching him a thing or two about the difference between true and false piety, and truth and falsehood in general.
He asks Orgon about Mariane's engagement to Valère. He is dismayed to hear that the marriage is postponed and that Orgon is planning "to be guided/ By Heaven's will" (1.5.35). He heads off to break the bad news to the family.
Much later, Cléante talks to Tartuffe about the recent falling out between Orgon and Damis. He asks Tartuffe how he, as a man of God, could not only allow Damis to be banished, but accept his inheritance as well. He questions Tartuffe's justifications for accepting the money and marrying Mariane.
He fails to make Tartuffe reconsider his position.
Cléante tells Orgon that he probably shouldn't have given Tartuffe access to the documents in his strongbox.
When Orgon tells Cléante that, from here on out, he'll hate all pious men, Cléante tells him he's acting like an irrational baby.
When Damis comes in, ready to beat up Tartuffe, Cléante tells him to stop acting like an irrational, hotheaded baby.
Cléante reminds everyone that Tartuffe is planning his revenge, and that they should probably come up with a plan.
When Monsieur Loyal shows up, Cléante tells Orgon to treat him cordially and hear him out. Once Loyal has said his piece – and made everyone angry with him – Cléante takes charge, asks for the eviction notice, and tells him to leave.
Cléante tells Orgon to go away with Valère, and promises to take care of the family in his absence.
When Tartuffe tells everyone that he has ratted out Orgon as a traitor in order to best serve the King, Cléante confronts him, asking how he could accept the inheritance of a supposed criminal. Tartuffe has nothing to say to this.
Cléante stops Orgon from yelling at Tartuffe, and tells him that he should, instead, hope that the hypocrite truly repents and finds God.