Lady Catrina and her strange servant Jonas arrive in Camelot, where they are welcome to stay by a most delighted king Uther, who becomes captivated by his latest guest. Arthur, on the contrary, far from sharing his father's enthusiasm and in the sight of the flirting going on, is pretty appalled with the situation. Merlin and Gaius have the feeling that she is not what she seems and their suspicions are proven true when Merlin discovers that Lady Catrina is a troll and that unfortunately, her intentions are far beyond the prize of a king's heart. Horrified, he reveals the truth to Arthur, who doesn't believe him. Merlin embarks in the task of proving the real nature of the woman while at the same time saving Uther from ruin and Camelot from fall. Will the young warlock be able to overcome the powerful magic of the troll before it's too late?

Peace talks are held at Camelot when dignitaries from rival kingdoms arrive. King Alined is determined there will be no peace though and will use magic to make sure his wishes happen.

Lady Catrina has now been crowned and is now known as Queen Catrina. She accuses Merlin of stealing and he is driven into hiding, and must now find a way to expose her true form.

Gwen is mistaken for Morgana and kidnapped by the savage outlaw Hengist. Uther refuses to pay her ransom, so Arthur defies his father and heads out into dangerous enemy territory to fight for Gwen's freedom. Merlin suspects Arthur's devotion to Gwen is more than that of a prince to one of his subjects. How will Arthur react when he discovers Gwen is not alone in Hengist's castle? She and Lancelot have found each other again, and powerful feelings rekindle.

Merlin finds himself becoming friends with Morgana when he helps a boy stay hidden. The two of them try to get the boy back whence he came, but things turn bad when Uther announces that anyone helping the boy will be executed.

Merlin is told by the Great Dragon that it is his destiny to make sure that the young Prince Arthur is kept safe. Anybody caught performing magic is punished with death and Merlin is not a fan of Arthur. When Arthur's life is endangered Merlin finds himself tested.

When the Lady Morgana is struck down with a mysterious illness, Gaius is at a loss for a cure. Thankfully a new physician, Edwin Muirden is on hand to bring the King's ward back from the brink.

Arthur is determined to win an upcoming jousting competition at Camelot. Gwen challenges Arthur to give up his spoilt ways after he goes undercover with her and Merlin. Myror shows up at Camelot determined to kill Arthur. Arthur is determined to prove himself and win the contest unaware that he is in danger.

Morgana has a nightmare and sees Arthur's death at the hands of a strange but beautiful girl. Meanwhile, hunting in the forest, Merlin and Arthur save the same girl, Sophia, and her father, Aulfric from attack by bandits and bring them to Camelot for refuge. Morgana realizes that Sophia is the girl from her nightmare and tries to warn Arthur, who is smitten with her. As the truth of Morgana's magical gift for seeing future events unfolds, so does a father and daughter's plan to bring down the kingdom of Camelot by sacrificing Arthur in return for eternal life.

Gwen's father, Tom, helps a sorcerer named Tauren turn lead into gold using a magic stone. As Tauren escapes, Tom is caught and will await trial. Whilst looking for Gwen, Morgana finds the magic stone, and Merlin can sense it. When Tom is killed by Uther, Morgana is out for revenge on Uther.

When Morgana's nightmares spill into waking hours, she becomes terrified that she has the power of magic. Gaius is determined to keep her in the dark for her own good but Merlin won't stand by and watch his friend suffer. He knows exactly what she's going through and he knows she needs the truth. Is Merlin about to reveal his secret at last?

Freya is found by Merlin trapped in a bounty hunter's cage and decides to try and help her escape. Merlin refuses to listen to Gaius' warnings not to get involved. After freeing her Merlin hides Freya in the tunnels beneath Camelot. Merlin is forced to make some hard decisions to keep Freya safe.

Alvarr is determined to allow magic to be used gain and destroy Camelot. Alvarr needs to reclaim the Crystal of Neahtid to make his plan work. Alvarr and Morgana try to get their hands on the crystal and use a druid boy to help them. Merlin is surprised when he finds out the real power of the crystal.

A mysterious illness draws Merlin to a distant village. But it soon becomes clear that there is more at stake than just his patients' well-being as something sinister turns the air sour. Far from home and with no-one to trust, Merlin becomes embroiled in a deadly game of cat and mouse. No longer sure who is the hunter and who is the hunted, can the young warlock survive long enough to uncover the truth?

Merlin is stunned when his mother, Hunith, turns up in Camelot--bruised, battered and desperate for help from Uther. She explains to Uther that a bandit named Kanen and his men have been attacking her village demanding all of their harvest or he will kill them. When Uther refuses to help, Merlin leaves Camelot to protect his mother and friends. To Merlin's surprise, Arthur, Morgana and Gwen join forces with him to save his village--but at what cost?

An old flame of Gaius' arrives in Camelot under the influence of a Manticore.

Uther pressures Arthur into an arranged marriage with a visiting princess, Elena, though Merlin soon has reservations after discovering that Elena may not exactly be who she claims to be. As he tries to uncover the princess' dark secret, he learns that Elena's nanny is a Pixie. But what are their motivations? Who do they work for? And most important of all, what benefit do they get from her marriage to Arthur, the heir to the throne of Camelot? Will Merlin be able to get to the bottom of it all and prevent Arthur from making the biggest mistake of his life?

Camelot is hosting its annual sword tournament and knights from throughout the realm have come to compete for its coveted title. Amongst those hoping to win the crown is Knight Valiant.

A deadly plague spreads through Camelot. When it seems that sorcery can be the only possible explanation, Merlin and Gaius race to find a cure, while Gwen is arrested and sentenced to death for practising witchcraft.

Merlin is saved from a terrifying winged beast by a heroic stranger- a young man named Lancelot, who dreams of becoming a Knight of Camelot. In order to thank him, Merlin provides falsified records of Lancelot's noble birth and Lancelot is accepted. However, with the winged beast- discovered to be a Griffin- still on the loose, Merlin's decision could have far-reaching consequences not just for Lancelot but for Camelot...

New servant Cedric muscles in on Merlin's position as Arthur's right-hand man, and turns the prince against his loyal friend. Merlin is convinced the slippery newcomer is up to something, and he is right - Cedric is a conman and a thief who is after a magnificent jewel, recently unearthed in a tomb far beneath Camelot. Little does he know, his precious prize is more dangerous than he could possibly imagine. Camelot has never been more vulnerable, but how can Merlin make things right when, thanks to Cedric, he might have lost Arthur's friendship for good? Merlin faces the prospect of turning to the one creature he swore he would never trust again - The Great Dragon.

Gwen faces an impossible dilemma when she is forced to choose between saving the life of Elyan, her estranged brother and only sibling or Arthur's, Camelot's prince and the love of her life. When one of them is certain to find death at the hands of Cenred, who will Gwen choose? Once again, loyalty, love and friendships are tested to the limit as Arthur, Merlin and Gwen are forced to put their minds together to try and find a way out of the cruel quandary. Morgana and Morgause, in turn, will do their best ruin their plans. Will good conquer evil or will Gwen end up losing someone she loves again?

Camelot's legendary tournament only has one rule: there are no rules whatsoever. Terrifying warriors start to fill the mythical city, Gilli between them. Despite his small stature, Gilli is ready to join the action and committed to achieve victory with a secret weapon to help him: magic. When Gilli begins to realise the full extent of his powers, Merlin becomes torn since his new friend is putting his own life in danger as well as threatening the very heart of Camelot with his actions. Will Merlin be able to make Gilli see sense before it's too late?

In his determination to rule magic out of Camelot forever, Uther hires the services of Aredian, a terrifying witch hunter who is most feared due to the fact that he stops at nothing in the quest to uncover all and every kind of sorcery. Even though no one is under direct suspicion, several people in Camelot are afraid that the witch hunter could see straight through them: Morgana is worried that Uther might have her executed and Gaius is concerned for the fate of Merlin and his own, since caring for the young warlock is considered crime and treason. Will all three be able to escape a dreadful fate?

For the first time in over 300 years the fires of Idirsholas burn and Gaius is worried that a sorcerer has revived the deadly Knights of Medhir. Morgause returns and is determined to end Uther's reign at Camelot.