Merlin, a wizard on the cusp of adulthood, arrives in Camelot hoping to find a use for his magical powers. Instead, he learns that King Uther Pendragon, ruler of Camelot, despises magic and will sentence to death anyone who practises the art. Mary Collins' son is executed for this very reason, so she warns Uther that he soon will share the tears she has shed. She then incants a spell to cast herself away before he could intervene. Uther orders a festival to celebrate 20 years of peace in Camelot as a result of the ban on magic. Later, he argues with his ward Morgana, who warns him that he will only make enemies by continuing to persecute those who use sorcery.
Soon after, Merlin meets Gaius, the court physician, whose life Merlin saves when he falls from a balcony. Although Merlin denies it, Gaius believes he has magical powers, yet promises not to tell the king of these alleged actions. Merlin is soon given a room and Gaius realises that he has been sent to Camelot to be protected. Meanwhile, Mary Collins uses voodoo to kill Lady Helen, a famous singer scheduled to perform at the festival. She assumes Lady Helen's appearance, but her true form can still be seen in any reflection.
As Merlin sleeps, he hears an ominous voice saying his name repeatedly, and he soon awakes. At breakfast, Gaius purposely knocks over a bucket of water so that Merlin would use his powers to prevent it from falling. Gaius, having discovered Merlin's secret, warns him never to use his powers or he could be killed.
Merlin watches Arthur bully the servant Gregory, and tries to stop him. After he discovers that Arthur is the king's son, he is locked up for the night, and hears the same ominous voice calling his name. Gaius arranges his release, but Merlin is punished by being placed in the stocks, to have fruit and vegetables thrown at him. He meets Morgana's lady in waiting, Guinevere (Gwen), who shyly flirts with him. Gaius asks Merlin to deliver some potion for Lady Helen's voice. Merlin enters her room and there's no Helen; Merlin spots a voodoo doll and a book of enchantments, he begins to open it when he hears a door open and Lady Helen enters. Merlin hands the potion to her. Mary Collins watches him suspiciously as he leaves.
Merlin walks past Arthur and urges him into a fight using flails. Merlin uses his powers in order to win, though ends up losing when he notices that Gaius is watching the combat. Arthur realises there is something different about Merlin that he can't put his finger on, so decides to spare him.
Mary Collins, disguised as Lady Helen, arrives and is greeted by the king and dines with him. She comments on how it can't have been easy for Arthur growing up without a mother, and how the bond between mother and son is so hard to replace, alluding to her dead son. She then states that she is looking forward to her performance the following day.
Merlin is once again awoken by the same voice and decides to follow it, and ends up in a cave beneath the castle where The Great Dragon is imprisoned. He is told that he was given his magical gift for a reason, and that his destiny is to protect Arthur. Merlin argues against this, but soon learns that without him, Albion would fail to exist. The next morning, he is awoken by Gaius who asks him to deliver medicine to Morgana who is suffering from nightmares. Merlin arrives in Morgana's quarters only to find her changing her clothes. She mistakes Merlin for Gwen, who arrives just in time to stop Morgana noticing who she's been talking to. Merlin thanks her and runs out of the room.
Lady Helen is given a complimentary basket of fruit, but her secret is revealed after the servant unveils her purposely blanketed mirror. The servant is then killed. Helen exits the room, prepared for the performance ahead. As the ceremony begins, Lady Helen of Mora arrives and sings. Her song puts everybody but Merlin under a sleeping spell (he covered his ears with his hands) - she's unaware he's unaffected. As the room becomes dark and coated with cobwebs, she unsheathes a dagger with which she plans to kill Prince Arthur. Merlin intervenes, using his powers to lower the chandelier onto Lady Helen. She is crushed, so the sleeping spell wears away and all spectators are awoken. Mary Collins's form of Lady Helen has also faded, and on the brink of death, she throws her dagger at Arthur. Merlin intervenes once more, using his powers to slow time in order to save Arthur from the incoming blade. He is saved, and Mary Collins dies. Merlin is appointed Arthur's manservant by the king, despite them both being upset by the idea.
In the final scene, Gaius gives Merlin a book of magic to study in secret, and Arthur calls for Merlin's first day of duty.