Here is a brief plot summary of Troilus & Cressida:
In Troy itself, King Priam and his sons, the general, Hector and his brother Paris, whose theft of Menelaus’ wife, Helen, had started the war seven years before, are arguing. Their priestess sister, Cassandra, prophesies destruction for all while their younger brother Troilus is not paying attention to the conflict as he has met and fallen in love with Cressida, whose father, Calchas, has defected to the Greek camp.
Cressida’s uncle, Pandarus, assists the lovers to consummate their union but on the same night there is an exchange of prisoners and despite her protests Cressida is sent to join her father in the Greek camp, swearing eternal loyalty to Troilus.
A challenge from Hector is answered by the Greek hero, Ajax, but Hector withdraws as Ajax is related to his family.
In the Greek camp Cressida is pursued by Diomedes. She is confused by what has happened and believes that she’ll never see Troilus again. Not knowing that Troilus has secretly left Troy to seek her, she responds to Diomedes. Troilus and Ulysses overhear their encounter and Troilus realises that his love has turned against her vows of faithfulness, and he returns to the city to fight more determinedly against the Greeks.
In the final battle Hector kills Patroclus and Achilles is finally provoked by this death to join the fighting. At first overcome briefly by Hector, but spared, Achilles succeeds in trapping the great champion and Hector, unarmed, is slaughtered by Achilles’ troop of thuggish soldiers, the Myrmidons. Troilus swears revenge for his brother’s death, and mourns the end of his innocence with the loss of his beloved Cressida.