This drama is adapted from the story of King Arthur and the magician Merlin, and is jointly produced by BBC Wales and Shine Films. Merlin (Colin Morgan) was taught by his mother to come to the palace from his hometown to find Gaius, the head court physician, to learn skills. There, magic was strictly prohibited by the king. The secret of Merlin's magic was discovered by Gaius. Not only did Gaius not blame him, but he also adopted him as his adopted son and advised him to use his talent for the right way. Merlin also encountered an ancient dragon locked deep in the castle. The dragon told him that he had a great mission, and this arduous task was to protect Prince Arthur and make Arthur the future king. In order to protect him by Arthur's side, Merlin became Arthur's personal valet. But things were not as smooth as Merlin imagined. The evil witch Nimueh discovered Merlin's great mission and tried to frame him...