Camelot is hosting its annual sword tournament and knights from throughout the realm have come to compete for its prize. Knight Valiant, determined to win this year's prize, visits a wizard who's created a magic shield for him. Painted with an elaborate snake motif, a few magic words make the snakes come to life and strike at his command. The wizard says that one bite will paralyze his victims so Valiant can finish them off. He hands Valiant the shield and tells him the snakes will do anything he commands. As thanks, Valiant commands the snakes to kill the wizard.
Valiant rides to Camelot and registers for the tournament. Meanwhile, Merlin spars with Prince Arthur to help him prepare for the tournament. Merlin isn't much help, as he's no match for Arthur's sword skills. A battered Merlin returns home to an amused Gaius. However, when Merlin uses magic, which is banned in the kingdom by punishment of death, to open a book about tournament etiquette, Gaius scolds him about being cavalier. Merlin complains about the huge list of tasks that being Arthur's manservant requires. Gaius says that Arthur has his tasks too, and that being a future king puts him under a lot of pressure.
Gwen, a blacksmith's daughter, gives Merlin a tutorial on the different pieces of armor so he'll be prepared. The morning of the tournament, Merlin dresses a nervous and impatient Arthur. King Uther opens the three-day tournament by addressing the competing knights. When he mentions that Arthur is the defending champion, Valiant turns around and meets eyes with the prince. The prize, aside from the title, is 1000 gold pieces. Uther declares the tournament open to a cheering crowd. He whispers to Arthur, "I trust you will make me proud."
Arthur handily defeats his first opponents as does Valiant, who doesn't have to use his magic shield this early in the game. During a break, Valiant congratulates Arthur on his victories. Arthur does the same. When Valiant's out of earshot, Merlin calls him a creep. They share a laugh, until Arthur remembers that he's a prince and Merlin is his manservant. He goes cold, giving Merlin a long list of chores to complete. At home, Merlin uses magic to multitask while studying the book of magic that Gaius gave to him. That is, until Gaius almost busts him when he tells him supper is ready.
At the castle during the reception, Valiant meets Morgana, the king's ward. He's taken with her, and as Arthur looks on, pours on the charm. He says that he understands the winner gets to escort the king's ward to the feast, so he intends to win. Morgana can't help but be smitten. Arthur calls her on it, and she accuses him of being jealous. He rudely denies that, saying there's nothing to be jealous of. After he departs, Morgana tells Gwen that she hopes Valiant wins the tournament. When Gwen says she can't mean that, Morgana says, "Actually, I do."
The next morning, Merlin is retrieving Arthur's armor when he hears snakes hissing. When he looks toward the source of the sound, Valiant's shield catches his eye. He examines it, and one of the snakes winks at him. Valiant catches him and confronts him, but Merlin says he was just gathering Arthur's armor. When Merlin presents the newly polished armor to Arthur, he's impressed but offers minimal compliments. Just before day two of competition begins, Gaius sees Merlin enjoying the festivities and teases him about actually enjoying himself. Merlin admits, "It's not totally terrible all the time."
Arthur defeats his opponent, but Valiant is having a tougher time against Ewan, his opponent. He knocks Ewan to the ground, then kneels on him and commands his snakes to strike. Ewan is shocked when the shield comes to life and bites him. When he becomes immobilized by the poison, Valiant strikes him unconscious. At his home, Gaius tends to the injured knight, and notices the snake bite on his neck. He shows Merlin, and both are confused at how he got it. Even worse, Gaius needs to find the snake that bit him to create an antidote. If he doesn't, Ewan will die.
Merlin remembers that he was fighting Valiant and acts on a hunch. He sneaks to his quarters and peeks inside, where he sees Valiant feeding live mice to the snakes on his shield. Alarmed, he runs back home and tells Gaius what he saw. When Merlin wants to tell King Uther, Gaius cautions him about accusing a knight of using magic to cheat until he has proof. He tells Merlin that his word alone will mean very little to a king.
The next day, Arthur fights a gigantic opponent, but Arthur is quicker -- he tires out the slower man and wins. When Valiant wins his match, it becomes clear that Valiant and Arthur will face off in tomorrow's final. That night, Gaius tells Merlin he was right; they can't let Valiant get away with cheating and worry he'll kill Arthur. If they can get the antidote, Ewan will recover and can tell Uther about the snakes. While Valiant is at dinner, Merlin sneaks into his quarters. When one of the snakes comes to life, he decapitates it and takes the head. Valiant sees him running away.
Gaius milks the venom from the head and starts on an antidote. He tells Merlin that he was very brave to do what he did. Merlin takes the head to Arthur and tells him that Valiant is cheating. Arthur is dubious that Valiant's using magic in Camelot, but Merlin tells him to look at the snake's head. He asks if he's seen anything like it in Camelot. Arthur can't deny it, and asks Merlin to swear that everything he's told him is true. Merlin swears, and Arthur says, "I believe you." Both are unaware that one of the snakes is spying on them from a rafter above.
The next day, Ewan wakes and is assured by Gaius that Arthur has been warned about the snakes and has requested an audience with the king. Gaius leaves Ewan to rest while he gets more herbs. While he's gone, a snake slithers into Ewan's bed and bites him again, this time killing him. Gaius returns home to find him dead.
Arthur requests an audience with the king about Valiant's cheating where he accuses the knight of using a magic shield. Valiant calls the accusation outrageous and demands proof. They show Uther the snake's head, and Arthur says that Knight Ewan will testify to what he saw. Gaius tells Merlin that Ewan is dead. When Arthur learns of Ewan's fate, he relays it to his father. Uther becomes furious when he learns Arthur took the word of his servant against a knight. When Merlin says he saw the snakes come alive, Uther chastises him for interrupting and has him seized by the guards.
Valiant requests for Merlin not to be punished on his behalf. At that, King Uther further chastises Arthur, saying that this is how a true Knight behaves, with gallantry and honor. Citing that Arthur lobbed the allegations because he's afraid to fight him, Valiant offers to let Arthur concede the tournament to him. Arthur refuses, but apologizes to Valiant and withdraws his accusations.
Arthur, humiliated that the king and entire court now think he's a coward, fires Merlin for making him look the fool. Merlin goes to the Great Dragon's cave and tells him that he's got the wrong person, as Arthur hates him now. The Great Dragon says he cannot hate the half that makes him whole and that this isn't the end, but the beginning. The riddles further frustrate Merlin, but that's all the Dragon is offering.
Gwen finds Merlin and asks him if it's true that Valiant is using magic. When he confirms it is, she asks him what he's going to do. Merlin wonders why everyone thinks it's up to him to do something. Gwen says he has to show everyone he was right, but doesn't have any ideas as to how he'll do it. Merlin wallows in despair until he spots a statue of a dog and gets an idea. He wheels the statue into his room and searches for spells to bring it to life. He attempts the same incantation several times, to no avail.
Frustrated at his lack of progress, Merlin warns Arthur not to fight in the tournament tomorrow, as Valiant will use the shield against him. Arthur knows that Merlin is telling the truth, but still refuses to concede the tournament because his people will think he's a coward. How can he expect men to follow a coward into battle? When Merlin says he'll die, Arthur is willing to accept that fate. It's his duty.
The morning of the final arrives. Arthur still can't bring the statue to life. At the castle, Morgana, who had nightmares about snakes the night before, helps Arthur dress for the tournament to offer encouragement. She tells him to be careful. Arthur enters the ring to a cheering crowd, excited to see the final. Meanwhile, Merlin brings the statue to life in the form of a Rottweiler. He warns Gaius not to go in his room, and rushes to the stadium. Gaius can't resist, and peeks, only to be greeted with a ferocious bark from the dog.
Arthur and Valiant fight a fierce battle. Arthur knocks Valiant's helmet off then thrills the crowd when he removes his own. During a struggle, Valiant disarms Arthur. When Arthur is at a safe distance, Merlin casts the spell. The snakes come out of the shield to everyone's shock, including Valiant's, who asks them what they're doing. "I didn't summon you." His secret out, he releases the snakes and commands them to kill Arthur. Morgana tosses him a sword, and he decapitates the snapping pythons. He attacks Valiant and skewers him with his sword. "Looks like I'm going to the feast after all," Arthur says, just before Valiant drops dead. The crowd wildly applauds his bravery.
At the feast, a proud Uther presents the champion, his son Prince Arthur. Morgana accompanies him and asks if his father will apologize for not believing him. "He'll never apologize," Arthur says. She says it's not every day a girl gets to save her prince. Chuffed, Arthur denies she saved him. She accuses him being unable to admit he was saved by a girl. Goaded, he says he didn't need help at all, and they angrily part company. Arthur tells Merlin about Morgana's audacity. "Like I needed any help," he arrogantly states. He then apologizes to Merlin and reinstates him as his servant, reeling off a long list of chores.