As our play opens, we meet Cassandra, a Trojan princess, daughter of King Priam and Queen Hecuba, cursed by Apollo to have the power of prophecy but never be believed, who sets the scene, describing the years of war caused by her brother Paris stealing Helen from the Greek commander, Menelaus. Troilus, also brother to Cassandra, is madly in love with Cressida, who remained in Troy when her father Calchus defected to the Greeks, but he can’t seem to connect, so he asks her uncle, Pandarus, to play matchmaker. Pandarus sings Troilus’s praises to Cressida, as they watch the Trojan and Greek soldiers parade, but she hides her feelings, not wanting to risk getting hurt, or seeming too forward.
Meanwhile, at the Greek camp, general Agamemnon and his commanders Ulysses, Nestor, Menelaus and Diomedes are grousing about the never-ending war. Their great soldier, Achilles, is refusing to fight. Instead, Achilles spends his time hanging around his tent complaining about his Greek commanders with his pal Patroclus, and Thersites, a scurrilous Greek servant. Ulysses and Nestor hatch a plot to make Achilles jealous by proclaiming that there will be a lottery to determine who will fight the Trojan prince, Hector (brother to Troilus and Paris). When Ajax and Achilles learn of this, havoc ensues. The Greeks do their best to foster this havoc, praising and pandering to Ajax, and ignoring Achilles.
Back in Troy, King Priam argues with his sons, Hector and Paris. Paris had stolen Menelaus’s wife Helen seven years previously, starting the Trojan War. The arguments concern whether they should return Helen and end the conflict. But they decide to continue fighting. The princes’ sister, Cassandra, prophesises destruction for all. Their younger brother, Troilus, is increasingly distracted from the conflict by his love for Cressida.
Cressida’s uncle, Pandarus finally manages to get Troilus and Cressida to connect. They proclaim their love and all seems to be going well, but that same day, Cressida’s father arranges to exchange his daughter for a Trojan prisoner. Despite her protests, Cressida is sent away to join her father. Cressida and Troilus swear eternal loyalty to one another.
The day of the “Hector vs. Greatest Greek Warrior” dawns, and Cressida arrives at the Greek Camp, accompanied by Diomedes, who seems to have appointed himself her protector, and who rescues her when the Greeks get a little too snarky. The Trojans enter the camp to learn that the commanders have set Ajax to fight rather than Achilles. But no sooner than they begin the duel than Hector withdraws from the fight because Ajax is related to his family. Achilles invites the Trojans to his tent to party. Meanwhile, the Greek slave Thersites rails against all mankind and the stupidity of war and conflict.
As the post-fight festivities wind down, Troilus has secretly crept away to find Cressida. Cressida does not know that he is near, and Troilus and Ulysses overhear as she talks to and flirts with Diomedes. Heartbroken, Troilus realises that Cressida has broken her vows of faithfulness. He returns to the city to fight against the Greeks.
In the final battle, Hector kills Patroclus, motivating Achilles to finally join the fighting. While originally overcome by Hector, Achilles succeeds in trapping him. Hector, unarmed, is slaughtered by Achilles. Troilus swears revenge for his brother’s death and also (inwardly) for the loss of Cressida and his youthful innocence. Pandarus, Cressida’s uncle, cynically ends the play. He sees no hope for a world where politics overrule the desires and needs of the individual.