text: The prophet Calchas correctly determines the source of the troubles but will not speak unless Achilles vows to protect him.Achilles does so, and Calchas declares that Chryseis must be returned to her father.Agamemnon consents, but then commands that Achilles' battle prize Briseis, the daughter of Briseus, be brought to him to replace Chryseis.Angry at the dishonour of having his plunder and glory taken away (and, as he says later, because he loves Briseis), with the urging of his mother Thetis, Achilles refuses to fight or lead his troops alongside the other Greek forces.At the same time, burning with rage over Agamemnon's theft, Achilles prays to Thetis to convince Zeus to help the Trojans gain ground in the war, so that he may regain his honour.As the battle turns against the Greeks, thanks to the influence of Zeus, Nestor declares that the Trojans are winning because Agamemnon has angered Achilles, and urges the king to appease the warrior.Agamemnon agrees and sends Odysseus and two other chieftains, Ajax and Phoenix.They promise that, if Achilles returns to battle, Agamemnon will return the captive Briseis and other gifts.Achilles rejects all Agamemnon offers him and simply urges the Greeks to sail home as he was planning to do.The Trojans, led by Hector, subsequently push the Greek army back toward the beaches and assault the Greek ships.With the Greek forces on the verge of absolute destruction, Patroclus leads the Myrmidons into battle, wearing Achilles' armour, though Achilles remains at his camp.Patroclus succeeds in pushing the Trojans back from the beaches, but is killed by Hector before he can lead a proper assault on the city of Troy.After receiving the news of the death of Patroclus from Antilochus, the son of Nestor, Achilles grieves over his beloved companion's death.His mother Thetis comes to comfort the distraught Achilles.