Arthur and Merlin discover the long-missing Morgana and returning her to Camelot. Shortly after her return, however, Uther's mind begins to fray. Merlin suspects it's due to someone's magic and puts himself in danger while investigating its source. (TV Guide)

With his father sidelined with insanity, it's left to Arthur and his knights to defend Camelot from the invading Cenred. A poisoned Merlin tries to stop Morgana. (TV Guide)

Merlin accidentally releases a mischievous goblin from a secret chamber that takes possession of Gaius, leading the physician to develop a hankering for gold, ale and magical jokes. (TV Guide)

Merlin and Arthur are rescued from a tavern brawl by the enigmatic Gwaine, who's injured during the melee. They take him to Camelot to recover, and he's soon drinking, wooing the ladies and causing trouble. (TV Guide)

Merlin tries to alter fate after the sorcerer Taliesin takes him to a crystal cave and gives him a glimpse into the future: Morgana about to kill Uther. Merlin's efforts to change destiny have fatal consequences, however, leading him to try and undo the damage he caused. (TV Guide)

Arthur is pressured to marry a visiting princess. Merlin has his doubts about her, however, and his suspicions may be proved right when he discovers that her nanny is a pixie. (TV Guide)

Gwen faces the impossible dilemma of choosing between Arthur and her estranged brother, one of whom is sure to die at Cenred's hand. She works with Arthur and Merlin to find an out, but Morgana and Morgause do their best to waylay their plan. (TV Guide)

Arthur tries to prove himself a worthy heir to Camelot by embarking on a quest to retrieve the Golden Trident from the Fisher King. Before he leaves, however, Morgana gives him a bracelet that zaps him of his strength. (TV Guide)

Gaius reunites with an old flame, but Merlin soon learns that she's under the spell of a Manticore and involved in a plot to kill Uther. His smitten mentor, however, will hear none of it, leaving it to the young wizard to figure out how to convince Gaius of the truth and avert disaster. (TV Guide)

Morgana's fear of Gwen becoming Camelot's queen leads her to reveal Arthur's courtship of the servant to Uther, who banishes her. But when Arthur vows to leave the kingdom with her, Morgana ups the ante and frames Gwen for using magic on the prince, causing the king to condemn her to death. (TV Guide)

A young man of small stature advances through Camelot's annual tournament thanks to a magical ring. Merlin fears that not only is he putting his own life in danger, but also the kingdom as a whole, for he's fated to face an opponent who dares not lose: Uther. (TV Guide)

Arthur and Merlin are captured by a slave trader while trying to retrieve the Cup of Life, a magical goblet that can give the gift of immortality through magical means. Although Arthur and Merlin escape, the Cup falls into the possession of Morgause, who uses its power to create an immortal army to take on Uther. (TV Guide)

The Season 3 finale finds Camelot crumbling under the control of Queen Morgana and Morgause's immortal army. While Arthur, Lancelot, Elyan and Percival prepare a counterattack, Merlin rushes to retrieve the Excalibur sword from the Lake of Avalon. (TV Guide)