As a result, when the disguised Merlin tried to heal Uther, the magic was reversed and ended up killing him. Mordred assists in the escape, and is knighted for his bravery.
He had a deep hatred for Camelot, stating "no friend of Camelot is innocent". As Arthur retook Camelot, Percival and Leon freed the prisoners. Morgana, it transpires, has been mortally wounded in the battle and escapes the castle. While Merlin sincerely wants to help her, the warnings of his guardian and Kilgarrah hamstring his intentions, and his fears eventually impact on their relationship; but he advised her to visit the Druids and she does, where one confirms her worst fear - she has magic.
Now, more crazed than ever to kill Arthur, Morgana travels to the Lake of Avalon after learning that Merlin is attempting to save Arthur there.
While working against the kingdom from the outside, Morgause sent her half-sister to serve as a spy and occasional assassin within the royal household itself. Then, while Uther was incapacitated, Morgause invaded Camelot with the army of her ally, Cenred, a king of a neighboring kingdom. He returns at the beginning of the fourth season to help Merlin fight the Dorocha spirits released by Morgana.
But Elyan does have clues to where Gawain is; at Morgana's new hideout, Ruadan's castle. Elyan broke under the torture and revealed that Arthur was traveling to Ealdor and was locked in a cell with Gaius and Gawain. With Gwaine having been injured in the fight, Arthur had him brought to Camelot to treat his wounds. Morgana succeeds in turning Gwen against Camelot, and Gwen returns to the castle where she makes numerous attempts on Arthur's life under Morgana's orders.
Morgana has also abducted many of Arthur's knights and is using them as slaves to help her in her plans. Gwaine subsequently joined the two on their quest to recover the Cup of Life, but the Cup is lost during a subsequent attack by Cenred's forces. Alator realises from Gaius' words that Merlin is destined to unite the lands of Albion and bring peace to all those with magic and that Morgana is only destined to bring about darkness and tyranny to the land. As Gwaine helped Arthur face the monsters in the kingdom, Merlin confronted the Fisher King prior to his death, Arthur subsequently claiming the King's trident. Gaius tells Merlin she suffers from nightmares, and the young warlock often brought her the physician's latest sleeping draught. ), and ultimately kisses her before he goes to joust. The sorceress finally dies alone, returning peace to Camelot and Albion, although Arthur perishes minutes later. Elyan returned to Camelot, without much luck. After doing so, she betrayed Cenred, ordering one of his men to kill him because she no longer had any use for him. With Gwen's relationship with Morgana having cooled after Morgana's return to Camelot and her new allegiance to Morgause, Gwen has begun to spend more time with Merlin, assisting him when he was accused of sorcery while Gaius was possessed by a goblin.
He has an unfortunate habit, according to Arthur, of making up jokes about it. The second episode brings Mordred to the center stage as he journeys with the Saxons and the two prisoners—Arthur and Merlin—to the fortress in Ismere where Morgana is. She tells Merlin she can never face Arthur again leaving Merlin to tell Arthur of Morgana's plans.
When she visits Arthur to thank him for his kindness, she finds him doubting his father's love for him. When the mysterious hunter Julius Borden returned to Camelot to search for a dragon's egg, the Dragon warns Merlin to save it before Borden does any harm. In "The Tears of Uther Pendragon (Part II), Sir Leon helps defend the castle against Cenred's army and engages in combat with one of the undead soldiers summoned by Morgana, but Merlin breaks the spell reanimating the undead soldier before Leon is killed. Lancelot noticed this and decided to leave, considering Arthur more worthy of Gwen's hand. The execution was halted, however, when Merlin brought forth proof that Aredian had orchestrated the entire event by drugging the witnesses. The four eventually made it to Ealdor, where Arthur was treated for his wounds and had a brief moment of reconciliation with Gwen, who had since come to stay with Merlin's mother, Hunith. Cenred thought little of towns in the outlying regions of his kingdom, so when Later, Cenred broke the peace agreement with Camelot and his men attacked Morgana acted as a hostage and when Arthur attempted to rescue her, Cenred held a sword to her throat while Morgause attempted to kill Arthur with magic. In the premiere episode of the fourth series, "The Darkest Hour", Lancelot still held his position as a knight and was one of those who accompanied Arthur in the quest to close the veil between the realms of the living and the dead, which had been torn open by Morgana in her quest for revenge against Camelot.