Theseus tells of his childhood at his grandfather's court in Troizen. His mother is the only remaining legitimate child of the king, and Theseus knows nothing of his father. It is rumored that his father is Poseidon, the sea- god. At age seven he witnesses the Horse Sacrifice, and the King Horse, whom Theseus believes to be also fathered by Poseidon and therefore his brother, is sacrificed to the god. Theseus heads to the sacrifice with his mother, who, although only twenty-three, is the "Chief Priestess of Mother Dia." But his grandfather, the King, calls Theseus forward to go with him. They are honoring Poseidon, and the King is his head priest. His grandfather tells him that he will be dedicated to Poseidon after the sacrifice and that soon he will serve the god at his shrine in Sphairia. All of the people observe the rite. When the horse is killed, Theseus almost loses control of himself, but he maintains his poise. For the first time, hears a sound like a surging of the sea in his ears. He does not cry until he Is back at home with his mother. The next day, the King comes to speak with Theseus. He knows his grandson is angry that the King Horse was killed, but the King explains that the sacrifice was in honor of Poseidon, who long ago told the King Horse how to guide their people to the sea. He tells Theseus about moira, "the finished shape of our fate." Just as it was the King Horse's moira to be sacrificed, so it is the king's moira to sacrifice himself for the people when the god tells him to.
The next year, Theseus begins to serve Poseidon once every four months in Sphairia. He learns to live with the presence of the god. From deep inside the sacred spring, hears the sounds of Poseidon. After a year, Theseus whispers his worries and takes comfort in the god's responses. Another boy, Simo, comes to the shrine, and laughs at Theseus's claim that he is Poseidon's son. Theseus attacks Simo, but Theseus realizes that he is small for his age. He decides that he must outdo the bigger boys and continually takes risks, using his greater agility to perform tasks that they cannot. While playing with the Palace bull, one of Theseus's friends falls off a fence and Theseus saves his life. One day, when Theseus is ten years old, Simo begins to taunt him. Theseus warns Simo to stay quiet, for he senses that Poseidon is angry. The next moment there is an earthquake. Afterwards, Simo believes that Theseus is Poseidon's son. Theseus is content, because he now knows that the god has sent him a sign.
From the beginning of his life, Theseus senses that he is special. He does not question the possibility that he is Poseidon's son but rather seeks proof of what he believes to be true. Theseus realizes at a very young age the price that must be paid to be a king. The fate of a king is not unknown; it is preordained. Theseus recognizes that moira is the finished shape of his fate because there is a path that he must follow, and that path lies inevitably in front of him. Theseus understands the concept of moira when the King explains it to him. Theseus recognizes that moira does not mean that all events are predetermined or that he has complete free will. Rather, moira means that it is his duty to live in such a way that he fulfills his fate. He sees that he must act of his own accord and do his best to achieve our fate. At the same time, Theseus cannot escape our fate; the gods will not be cheated. Thus, the king must go to the god when he is called or else great harm will come to his people.
When he keeps his composure at the sacrifice, Theseus shows that he has the bearing of a king. Theseus believes that he is Poseidon's son even though he is physically small. He decides that he must prove himself worthy and begins to challenge other boys and himself to perform dangerous feats. Theseus does not assume that his heritage makes him better than others. Rather, works to become more powerful than all of the other youths. Theseus sees that the simple fact that Poseidon is his father does not mean that he deserves to have such a father. Theseus must demonstrate that he is worthy of his heritage. The gods' favor is not given freely; it must be earned. The novel suggests that the fate of one man is like that of a kingdom. Both must continually renew their pledge to the gods in order to maintain the goodwill of the powers that are beyond them. Theseus does his best to make his father proud of him as a son and this demonstrates that he also has what it takes to be a king, because he must be ready to do everything he can to make the gods look kindly upon his people.