Merlin would have been killed by a giant griffin (half eagle, half lion) if not for valiant Lancelot, who bravely attacked it and got them safely away. Learning Lancelot's life dream is to become a knight, grateful Merlin brings him to court, but when told only noblemen may apply, magically forges proof of nobility. Lancelot passes hazing and close combat tests against Prince Arthur but is found out as commoner and jailed. When the griffin attacks Camelot - even inside the royal castle - the knights' arms prove unable to penetrate it . Arthur frees Lancelot, who in return (with Merlin's magical help) triumphs where all knighthood fails miserably, but will Uther finally hear Arthur's plea to allow the best sword to serve in chivalry despite existing social restrictions?

Receiving tainted lilies collected by unsuspecting Gwen, royal ward Morgana falls ill with an unidentified brain disease Gaius can't cure. Mysterious healer Edwin's "remedy to cure all ills" seemingly works (by actually removing the cursed black beetle he hid in the lilies). As Edwin maneuvers grateful King Uther to instate him as new court physician, Gaius gets court archivist Geoffrey to allow him illegal access to the sealed records of Uther's purge of magic, revealing Edwin's parents as executed black sorcerers. After consulting the dragon (who says he must choose whether or not Arthur and Merlin's destined time has come), Gaius, taking a threat by Edwin to expose Merlin's magic, tells Merlin - the "son he never had" - that the time has come to step down. Edwin, now free to use another beetle, condemns Uther to an agonizing death like his parents but takes one monumental risk - a duel of magic with 'mere novice' Merlin.

A black knight crashes Arthur's coming-of-age ceremony, throwing down the gauntlet to any knight who will fight him, killing all who do, one day at a time. Gaius discovers he is Uther's dead brother-in-law, now a wraith summoned from the grave by the witch Nimueh, seeking revenge for the death of his sister who died giving birth to Arthur. His intent: to eventually fight and kill Uther. Merlin learns that only a special sword burnished with a dragon's fiery breath can kill the knight. To that end, he asks Gwen for the best sword her father ever forged (the sword later known as Excalibur) and asks the imprisoned dragon to burnish it. The Dragon, however, tells Merlin that, once created, only Arthur should wield it, as evil will come of it otherwise. Merlin gives his word. Unfortunately, Uther has Arthur drugged and locked in his room, preparing to face the wraith himself. With Excalibur in his hand, victory might come but would leave Uther in control of a powerful magical weapon.

Part One: An ugly old troll drinks a potion transforming herself into the glamorous Lady Catrina, who arrives at Camelot with her servant Jonas. Gaius, who has met the real Catrina, and Merlin, who witnesses her true identity, are unable to convince bone-headed Uther of Catrina's real nature, especially when she bewitches him by giving him a magic pendant. Merlin attempts magic to expose her but she is too strong and it is too late to stop her marrying the king and becoming the queen of Camelot.

Merlin spies on the troll and steals the potion she uses to resemble Catrina, replacing it with a fake one made by Gaius. Consequently she turns back into a troll, in view of everybody, but Uther, still bewitched by her, fails to see this. Merlin learns that the only way to break the spell on him is to make him weep real tears. Thus Gaius prepares another potion, which Arthur drinks, and makes him appear to be dead. This does the trick and the king finally comes to his senses. Arthur kills the troll and Jonas and thanks Merlin for his efforts.

When a mysterious warrior challenges Arthur to a duel, no one could possibly predict the devastating chain of events it sets in motion - least of all the young prince himself. Arthur and Merlin soon find themselves on a strange quest at the behest of the beautiful Morgause. Through her, Arthur discovers a dark secret which threatens to bring about the downfall of the kingdom.

Merlin finds a secret chamber and accidentally releases a Goblin, which wreaks havoc.

Arthur is pressured into an arranged marriage with a visiting princess, but there's more to her than mere gracelessness and a taste for frogs.

A healer is in Camelot using magic to heal the sick, and Gaius quickly realizes it is Alice, a woman whom he was about to marry many years earlier until she had to flee from Uther's persecution of sorcerers. Now Gaius is happy to work with Alice again in preparing potions, but he is unaware that Alice is being controlled by a mythical monster, a manticore, which urges her to poison the cold-hearted king. To break the manticore's hold over Alice and ultimately save her from execution, Gaius has to perform the magic that he possessed but had forsaken long ago.

Sir Leon is nursed back to health by Druids using the Cup of Life after he is the sole survivor of an attack by Cenred's men. It purportedly grants immortality to those who drink from it, and Arthur and Merlin retrieve it from the Druids to prevent it falling into Cenred's hands. However, they, along with Gwaine, are ambushed and the cup stolen. Having killed Cenred, Morgause makes his soldiers drink from it and, under her orders, they successfully attack Camelot. By the time the three young men arrive back at the court, Uther is in chains and Camelot has a new ruler.

The kingdom is on the brink of collapse, with Morgana poised to strike. As Lancelot races back to Camelot with the dying Merlin, Arthur must continue on his mission to vanquish the Dorocha without them. Though the knights know their journey to the Isle of the Blessed is fraught with danger, none anticipate the sacrifice Arthur intends to make there. Friendship and loyalty are tested to the limit, but in the end, it is the power of love that changes all their lives forever.

The mighty citadel is buzzing in anticipation of the prince's birthday celebrations, but Arthur's old adversary, Odin, promises to ensure this is one party Camelot will never forget, for amongst the assembling guests lurks a deadly assassin, set to strike. As the dust settles, Camelot is left devastated, but just how far is Merlin prepared to go to put things right? Would he really risk everything and reveal his secret?