The Homeric epic only covers a few weeks of the decade-long war, and does not narrate Achilles' death. It begins with Achilles' withdrawal from battle after being dishonoured by Agamemnon, the commander of the Achaean forces. Agamemnon has taken a woman named Chryseis as his slave. Her father Chryses, a priest of Apollo, begs Agamemnon to return her to him. Agamemnon refuses, and Apollo sends a plague amongst the Greeks. 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.