A Poet, Painter, and Jeweler come to Timon's house, hoping to sell him their wares, for Timon is a very generous man. Timon enters. He learns from a messenger that his friend Ventidius is in jail, so he sends money to pay for his freedom. He helps out several other citizens in need, and gladly accepts the works of the Poet and Painter and the jewels of the Jeweler. Apemantus comes to Timon's house, refuses a greeting, and scorns Timon's flatterers. Alcibiades arrives, and Timon greets him.

Timon throws a feast at his home, and all his friends are in attendance. Apemantus declares he has come merely to be an observer of the villainous flatterers who fill Timon's house. Timon speaks of his fondness for his friends and the pleasure he finds in giving them gifts, all without expectation of a return. Timon's servant Flavius worries that Timon will run out of money if he keeps being so generous. Most of Athens's citizens are amazed that Timon continues to be so generous, as it seems to them that Timon must have some magical power to possess such an unending bounty.

Three creditors, friends of Timon who lend him money, call their debts due, and send servants to Timon's door with bills in hand. Timon tries to dismiss them, but they won't be sent away. Timon asks Flavius why he has creditors at the door, and Flavius explains that Timon has no money and is in debt. Timon orders him to sell his land, but it is already mortgaged. Timon asks why Flavius never told him about the state of his affairs before, and Flavius insists that he had tried, but Timon always refused to listen. Flavius says that everyone loved Timon, but when his finances are gone, those who praised him will abandon him too. Timon doesn't believe him, and sends servants to ask his friends for loans, but Flavius says he has already tried that, and no one would lend him anything.

Each of three of Timon's servants arrives at one of Timon's friend's houses to ask for a loan, but each man refuses. Servants ask the newly released Ventidius for a loan also, but he refuses. Creditors' servants swarm around Timon's house, though they note how strange it is that their masters wear gifts from Timon while they demand payment on loans he took out from them in order to buy them gifts. Timon is enraged to be trapped in his house by groups of creditors' servants, and plans a last dinner party.

Timon invites all his friends and other Lords. Timon says grace over the covered dishes, asking the gods to be sure to never give too much to mankind, always hold something back, and to never ask for anything back, for mankind will abandon them. Then he reveals stones and boiling water. Timon curses the flattery of his alleged friends, and leaves Athens.

Meanwhile Alcibiades argues with the Senators about the fate of one of his friends, sentenced to death for having killed a man in a rage. Alcibiades tries to save his friend, but ends up annoying the senate so much that they banish Alcibiades. Alcibiades leaves, planning to raise an army to attack Athens.

Timon sets off into the wilderness. His servants mourn his departure, sad that someone could fall so far from being so generous. Flavius shares out his last money and sets off to serve Timon in the wilderness. Timon searches for food in the forest, only to discover a hidden cache of gold. Struck by the irony of his discovery now that he no longer needs it, Timon buries the gold again, keeping some. Then he is visited by all manner of men in the woods, starting with Alcibiades. When he hears Alcibiades's intention to destroy Athens, he gives him a donation in gold and urges him to massacre everyone.

Apemantus comes to Timon's cave in the forest and scorns him, remarking that his fall came about from being so generous to a bunch of no-good flatterers. The two insult each other, then Timon remarks that he is so miserable to have fallen because he never knew suffering, but Apemantus has, though he has never known such a horror as base flattery--so why does he hate humanity? Timon is the one who really has reason for such a response. The two men discuss their desires to turn the world over to the beasts, but end in insults, and Apemantus departs.

Then Flavius arrives, offering Timon his last money and weeping. Impressed at this show of pity, Timon realizes Flavius was the one honest man he came in contact with in Athens, and he is the one man who is able to escape his enthusiastic cursing of humanity. Timon gives him gold and orders him to leave.

The Poet and Painter have heard Timon has gold, so they arrive to ingratiate themselves to him. Timon sends them off on a wild goose chase. Later Flavius returns with two senators who announce that the people have determined Timon's treatment was unfair, and they want him to return to Athens. Timon refuses. The senators believe Timon's presence in Athens will somehow halt Alcibiades's invasion, but they can't shift Timon.

Alcibiades arrives at the gates of Athens. The senators attempt to defend the city, explaining that not everyone in Athens insulted Alcibiades and Timon, and they ask that Alcibiades come into the city in peace, without killing everyone. Alcibiades agrees, and punishes only those who have slighted himself and Timon. Then a soldier arrives with news that Timon has died, and Alcibiades reads his epitaph. Though he died thinking everyone hated him, Alcibiades honors Timon, a man much more admired in Athens than he believed.