When the soothsayer reveals that the plague is the result of Agamemnon's refusal to return Chryseis to her father, Agamemnon is furious that he has been publicly named as being responsible for the plague. He insists that if he is forced to surrender Chryseis, his rightful war prize, then he must be repaid with Achilles' war prize, Briseis.
However, Achilles is stunned by the public disgrace of having Agamemnon demand Briseis, and he refuses to accept the indignity that he feels Agamemnon has made him undergo in full view of all the soldiers. Thus, he announces that he is withdrawing all of his troops from battle. He will not fight, and, furthermore, he and his men will return to their own country as soon as possible.
Nevertheless, Agamemnon decides to appease Apollo; he will return Chryseis, his war prize. He sends her safely aboard a ship heading home, and then he sends his heralds to collect Briseis (Achilles' war prize) for him. Surprisingly, Achilles surrenders the girl without any difficulty.
Achilles, in despair, prays to his mother, Thetis, the sea-goddess asking her to use her influence with Zeus to ensure that the Trojan armies defeat his fellow Achaian soldiers. Achilles hopes that this result will cause disgrace for Agamemnon and so repay the wrong that the King did to Achilles.
Thetis visits Zeus on Olympos, and the king of the gods agrees to aid the Trojans, although he expresses a fear that his wife, Hera, will be annoyed because she is jealous of Thetis and hates the Trojans and hence cannot bear to see them win the war. Readers discover that Hera does indeed hate the Trojans, but she fears Zeus' wrath even more, and so she quiets her protests. The first book ends with a banquet of the gods in Zeus' palace.
