The story of Shakespeare's Troilus and Cressida, opens several years into the Trojan War. A prince of the Trojans and the son of the Trojan king Priam, Troilus is infatuated with Cressida, a beautiful local girl. Cressida’s father, the priest Calchas, has defected to the Greeks. Cressida has so far rebuffed Troilus’s advances, and so, Troilus contacts her uncle Pandarus to ask for his assistance convincing Cressida to be with him. Pandarus attempts to sway Cressida by praising Troilus more than some of the mightiest Trojan warriors when she can overhear him, but she appears unmoved. Secretly, however, she reveals she is, indeed, attracted to Troilus.
In the camp of the Greek army, the famous hero Achilles refuses to leave his tent, where he is living with Patroclus. Despite the fact that a war is going on and Achilles is their greatest fighter, he simply refuses to be drawn out. Ulysses and the other Greek leaders Agamemnon and Nestor gather to discuss this problem, which is infecting the entire Greek army with a lack of discipline and a dangerous sense of lawlessness. Ulysses reports that the greatest warrior on the Trojan side, Hector, has just issued a challenge to the Greeks for one-on-one combat. He suggests they appeal to Achilles’s vanity by selecting someone else to face Hector, implying that Achilles is not their greatest warrior. They hold a lottery and select Ajax, a mighty warrior but not in Achilles’s league.
In the Trojan camp, the military leaders discuss ending the war by returning the Greek princess Helen, whom their prince Paris kidnapped, sparking the hostilities. Troilus is horrified by this discussion, and after chiding his fellow Trojans, they decide to keep her, as sending her home now would be dishonorable. The prophet Cassandra informs the Trojans that the Greeks will eventually burn Troy to the ground, but once again, Troilus convinces everyone to keep fighting.
Troilus goes to Cressida’s house, where he is met by Pandarus, who escorts them to the bedroom to consummate their love. Once alone, Troilus and Cressida pledge their love to each other, promising to be faithful.
Meanwhile, Cressida’s father, Calchas makes a deal to trade his daughter to the Greeks in exchange for a Trojan prisoner. The next morning, Diomedes arrives and tells Cressida her fate, taking her away for the exchange. Arriving at the Greek camp, all the Greek military leaders line up to greet Cressida, making passes and touching her. Cressida responds warmly to each, except Ulysses, who, deeming her a wanton woman, refuses to touch her.
Ajax has become proud and puffed-up after his selection to fight Hector, which has the desired effect of making Achilles jealous. The Greeks and Trojans gather to watch Hector and Ajax fight, but the fight is postponed when Hector discovers that Ajax is half-Trojan; he refuses to fight a fellow Trojan. This moves the soldiers and a temporary truce is declared. The Greeks and Trojans decide to feast instead.
During the feast, Ulysses brings Troilus to Cressida’s tent to show him as she flirts with Diomedes and agrees to sleep with him. Troilus is crushed. He vows to kill Diomedes.
The next morning, the truce ends. Hector’s family begs him not to go to battle, as they have had a vision of his death. Hector ignores them. During the battle, Hector kills Patroclus, which drives Achilles to leave his tent, seeking to avenge his lover. Troilus and Diomedes meet on the battlefield, but their fight is a draw. Hector and Achilles meet, also ending in a draw.
Later, Achilles and his friends find Hector unarmed and alone. They murder Hector, and Achilles drags Hector’s mutilated body through the mud of the battlefield. The sight of their greatest hero dragged through the mud demoralizes the Trojans—except for the furious Troilus, who makes a bitter vow to destroy both Achilles and his Greek countrymen.
Pandarus approaches Troilus to see what he wants to do about Cressida, but Troilus is angry and abuses him, calling him a “broker” and beating him up. Pandarus addresses the audience, telling them that he is dying from his injuries, and asking for their pity because his efforts to bring two unfaithful lovers together has brought him nothing but misfortune. He informs them that he plans to pass all of his many diseases to the audience in his will, and they will all soon suffer and die like him.