Merlin's home village is besieged by raiders. They have intimidated a farmer called Matthew into giving them the village's entire harvest. The raiders' leader is Kanan, who is furious that Matthew kept back some of the food so the village wouldn't starve. He strikes Merlin's mother, Hunith, when she tries to stop the raiders; and demands the rest of the harvest in a week's time.
Hunith goes to Camelot to ask for help. The village lies in another kingdom but its ruler refuses to act. However, Uther will not intervene because by sending soldiers there, he would be declaring war. Merlin announces that he must return home to take care of his mother and Prince Arthur thanks him for his service. When Merlin sees Gwen to ask her for a sword, she and Morgana declare their intention to come with him and fight for his village.
Hunith makes Merlin promise not to reveal his magical abilities to anyone else. As they camp for the night, Arthur comes to join them. They reach the village and fight the raiders as they arrive. Kanan threatens the lives of everyone present, and orders his men to leave. Arthur tries to talk to the villagers but Merlin's old friend, William, objects. He is in favour of giving the raiders what they want so that no one will be killed. Arthur says that unless the local people fight, they will forever be at Kanan's mercy. The whole village rallies behind Arthur and William leaves furiously.
Merlin tries to talk to William, who believes that Arthur is risking their lives for the sake of military glory. Merlin says that Arthur is his friend and would not put innocent people in danger; William replies that a real friend would have told Arthur about his use of magic. After they go to bed, Arthur asks why Merlin came to Camelot. Merlin cannot bring himself to tell the truth and just says that he wanted to find somewhere where he could belong.
The next morning Hunith tells Merlin that she thinks Arthur truly likes him. Merlin says he would be dead if Arthur knew about his magic, but she disagrees. Merlin goes to collect wood and is cornered by William, who wants to know why Merlin will not use sorcery to defeat the raiders. Merlin insists it is his destiny to help Arthur become a great king, and William is enraged that Merlin would put Arthur before his own friends and family. Arthur trains the men of the village in basic combat. Morgana points out that the men are outnumbered and the women must also be allowed to fight, but Arthur rejects this suggestion. Merlin later overhears Gwen and Morgana admitting that both they and Arthur came with Merlin because they care about him.
Matthew, who was acting as a lookout, is killed and his body returned with a note from the raiders. It threatens that they will return tomorrow to massacre everyone in the village. William publicly accuses Arthur of responsibility for Matthew's death, then makes plans to leave before the raiders come. Merlin tries to stop him but William again says that Merlin is a traitor for refusing to use magic. Merlin explains to Arthur that William distrusts nobility because his father was killed while fighting in the service of a king. Arthur fears William is right that everyone will die if they are made to stay and fight. Merlin convinces him that he must have faith in the villagers or they will not find the strength to win the battle.
Guinevere stands up to Arthur when he tells the women to leave before Kanan returns. He agrees that they should remain to defend their home, and gives a rousing speech to the villagers. Hunith privately expresses her fear of Arthur discovering Merlin's secret. Merlin reassures her that if Arthur is a true friend he will still accept Merlin.
Arthur apologises to Gwen for not wanting the women to fight. She wants to say that she trusts Arthur, but stumbles over her words. Merlin tries to tell him the truth about his magic and is interrupted by Morgana, who informs them that the raiders have crossed the river. The raiders are lured into a trap (with the women setting fire to the fences, hemming them in while the men ambush them) and the villagers come out to fight. William returns and saves Merlin from being hit. As it looks like the village is losing the battle, Merlin uses his magic to create a strong whirlwind that sends the raiders fleeing.
Kanan remains and duels with Arthur, who runs him through with a sword. Arthur wants to know who used magic to bring the wind up. At this point Kanan uses his last moments to fire a crossbow in Arthur's direction. William pushes Arthur out of the way and is hit with the arrow. He is brought in to Merlin's house, where he confesses to being the sorcerer who conjured the whirlwind. Arthur leaves and William says that he wanted to give Merlin the chance to be the servant to a great king. He dies, and Merlin sobs over his body.
Arthur believes that what Merlin meant to tell him was that William was a sorcerer. He is upset that Merlin didn't warn him about something so dangerous. Merlin says goodbye to his mother and prepares to return to Camelot. Echoing the Great Dragon's words, she states that he and Arthur are like two sides of the same coin. She assures him that one day, when the time is right, he can tell the truth at last.