The novel begins the day after Arthur is conceived. Merlin awakes after being thrown from his horse to find that Duke Gorlois of Tintagel was killed in a fight. However, Merlin knows the fight occurred only because King Uther Pendragon wanted to sleep with Duchess Ygraine of Tintagel. Uther used Merlin and his “magic” to slip past the guards and to get Ygraine to sleep with him. Merlin has the gift of foresight, so he knows this union will result in the birth of the greatest king of England. The only stipulation to the agreement was that Merlin would raise the child as he saw fit. Merlin immediately goes into hiding at Bryn Myrrdin, a large cave he has made into his home.

A young boy, Ralf, brings word of Ygraine’s pregnancy. Since her own husband died, Uther made her his wife. Merlin was waiting for a summons from one of them to discuss plans for the illegitimate baby. Ygraine called upon Merlin first, and she said Uther was wary of the child. Uther was talking about plans to send Arthur to someone else, and Ygraine wanted Merlin to talk Uther out of his idea. Merlin and Ralf set out to find Uther on the battlefront. However, they come across Uther’s camp at a river crossing, and the two men talk. Merlin gives his word that the best thing for the child would be to have Merlin raise him in secret. If Uther doesn’t have another male heir, then Arthur would be the only Pendragon left to secure the throne. Uther comes to his senses and agrees. Months later, Merlin is called to Tintagel to be present for the birth of Arthur.

Merlin knows Uther’s enemies will believe the infant Arthur is with him, so Merlin leaves Arthur in the care of the woman who raised him. He leaves Ralf behind to watch for any danger that might befall Arthur. Merlin then leaves and travels east to Constantinople and beyond. While there, he receives a vision of a sword that belonged to Magnus Maximus, the first king of Britain. He doesn’t know where he will find it, but he realizes his visions are leading him to this sword. Merlin then gets word Uther is extremely sick and hasn’t yet produced another male heir. Merlin travels back to England and visits the King.

The King wants to know where Arthur is, and Merlin tells him Arthur was moved to Count Ector’s court; Ector was a good friend of Merlin’s father and an ally of the Pendragon throne. Merlin assured Uther than Ector could be trusted. Merlin leaves to go back to Bryn Myrrdin, but he knows many of Uther’s enemies will be spying on him. He must be careful not to lead them to Arthur. A group of spies sneaks into Merlin’s home to attempt to find Arthur. Merlin intentionally sends them on another path and immediately leaves to find Arthur.

While on his way, Merlin begins to get slightly distracted. He follows a number of signs that lead him to a tower, now in ruins. He investigates and finds a sword wrapped tightly. He knows this to be the sword he saw in his dreams, but he also knows the sword wasn’t meant for him. He then visits an old chapel sanctuary high above Ector’s home. When he arrives, he knows this place will hold a special meaning in Arthur’s future. He takes the sword to a lost castle in the middle of a lake and leaves it on an altar. Later, a young boy rides up to him at the sanctuary, and Merlin knows he is Arthur. However, he only reveals himself to Ralf and Ector. The others know him only as a lonely enchanter.

Arthur, now nine, becomes infatuated with Merlin and all his travels. Staying true to his word to help raise the boy, Merlin uses the time to teach Arthur about the ways of kings and helps develop his character. For four years their relationship builds, but Merlin does not tell Arthur about his true identity. One day, though, Arthur chases his hound and a stag to the castle in the lake. While he is away, a group of soldiers led by Cador, son of the dead duke Gorlois, finds Merlin. At first Merlin thinks they are going to kill him and Arthur. But when he realizes they are on his side, he knows Arthur is ready to join his father Uther in battle. Arthur had returned with the sword, but Merlin took it away and left it on the sanctuary altar for a later time.

The group arrives at the battle. Merlin visits a near-death Uther and tells him his son has arrived. Before they could begin the formalities, though, the Saxons attack. Uther, Arthur, and the others go into battle while Merlin watches from afar. The Saxons almost defeat the Britons and nearly kill Uther. At the last moment, Uther throws his sword into Arthur’s hand, and Arthur leads the army to victory. Merlin knows this show will secure Arthur’s place in the hearts and minds of the army, and they will know he is their true leader.

At the victory festival, Uther declares Arthur is his long-lost son and the heir to the Pendragon throne. Lot, an ambitious lesser king, says Arthur isn’t ready to be king. He says Uther should prove it by handing over his own sword, and thus the throne, to Arthur now. While in the act, Uther’s sword breaks and Uther immediately dies. Chaos ensues in the room, and the men argue over who should be king. So Cador mentions he saw Arthur with the most magnificent of all swords a few days earlier. Merlin mentions the sword is enchanted and only the true king can lift it. Lot then says they should see Arthur take the sword in person. The next morning, the entire camp leaves for the sanctuary. When they arrive, they watch in awe as Arthur takes hold of the sword and releases it from its stone-like wrappings. He is hailed as the true king of England.