Ransom is a modern adaptation of Homer's Iliad, which is the story of the last year of the mythical Trojan war. The narrative opens in medias res: after ten long, grueling years of combat against the city of Troy, Achilles is enjoying a moment alone on the beach, and his thoughts turn to his mother, a goddess of the sea. He also thinks of his son, Neoptolemus, and of his fallen close friend, Patroclus.
Achilles feels responsible for his friend's death because Patroclus was killed by Hector when Achilles wasn't in the battle to protect him. He had decided to withdraw from the battle, after Agamemnon, the leader of the Greeks, decided to take Achilles’ slave. To avenge Patroclus' death, Achilles kills Hector, and as Hector is dying, he predicts that Achilles will soon be dead as well. Achilles decides to defy the gods by mutilating Hector’s corpse, but every night, the gods restore his body as if it had never been violated. The end of the opening leaves the reader with the disturbing image of Achilles desperately trying to find peace by dragging the body of his enemy over the grave of his friend, but he can't change the past.
The story turns to Hector’s father, King Priam of Troy. Although the past eleven days have been focused on mourning his son, Priam also mourns the city and the toll that ten years of warfare has taken on the Trojans. In the middle of the night of the eleventh day, he is visited by the goddess Iris. She tells him to watch for chance, and when she leaves, he has a vision of himself and another man driving a chariot with a covered load. He finds Hecuba, his wife, and tells that he intends to pay Achilles to recover Hector. Burials are an important part of the Greek religious view of the afterlife, and so long as Hector's body is in the enemy camp, they can't properly mourn, and Hector can't begin his trek to the afterlife. Although both Hecuba and his court try to convince him differently, considering the danger involved, Priam insists on going through with his plan. They prepare the ransom to offer Achilles, find a simple cart and a cart driver named Somax (who has a mule named Beauty), and then Priam and Somax head to the Greek war camp.
While on the journey, they stop to rest on the banks of the Scamander River. Priam finds himself charmed by Somax and the simple passion the man shows for his life and family. As they prepare to cross the river, a young man appears to Priam and Somax and explains that he has been sent as an escort by none other than Achilles himself. Priam and Somax are suspicious but follow. After they cross the river, they realize that the young man is actually the messenger god, Hermes, which comforts Priam, as he realizes that the gods have blessed their quest.
An unseen force opens the gates so that Priam and Somax can go in. As Priam is approaching Achilles, Achilles feels a divine presence and falls to his knees, thinking that it’s his father Peleus. Though Achilles soon realizes the truth, the lingering feeling softens him towards Priam, who is able to talk with him, pleading from one father to another. Suddenly, in the midst of Priam’s persuasion, Achilles has a vision and agrees to exchange the body for the bounty. As Achilles retrieves the miraculously unscathed body and gives it to the laundry women to be prepared for burial, he finds himself comfortable with his enemies and even feels solidarity with Hector.
Achilles and Priam eat together as the woman prepare the body. They part amicably, and Achilles offers to respond if Priam calls for aid. Priam, in a moment of unusual cruelty, asks what will happen if Achilles is not alive in the end, to which Achilles responds simply that he will not come.
Priam and Somax only stop once on their journey back to Troy, so that the king can freely mourn his son in the privacy of the country. Back in the Greek camp, Achilles feels more peaceful about Patroclus as well. At sea, Achilles’ son sails for Troy. In the future, he will be the one to kill Priam (which is likely the vision that Achilles saw), but for now, those things haven’t happened yet. After the war is done and its biggest players have faded into legend, Somax lives into his old age. When he speaks of the time that he chauffeured King Priam with the help of Hermes to recover Hector’s body from the legendary warrior Achilles, no one believes him. For them, the most interesting thing about him is his mule.