After Morgana's determination threatens not only Arthur's future, but also the very balance of the world, Merlin faces his toughest challenge yet. Hellish creatures end up emerging killing everyone that they touch. With Uther a shadow of his former self, Arthur and his loyal knights, including Lancelot are forced to try and protect the kingdom.
The kingdom is on the verge of complete collapse and Morgana is poised to strike. Lancelot races back to Camelot with the dying Merlin leaving Arthur to continue on his mission to vanquish the Dorocha alone.
The city is looking forward with anticipation for the Prince's birthday celebrations. Arthur's old adversary, Odin, promises to make sure it will be a party that Camelot will never forget. A deadly assassin is lurking set to strike amongst the guests at the party. Camelot is left feeling devastated as the dust begins to settle.
Julius Borden shows up in Camelot with news of a magical secret that could threaten to change the landscape of the kingdom. He has found the final part of the key to the tomb of Ashkanar which is an ancient mausoleum which holds insode the last remaining dragon's egg.
Arthur discovers what it's really like to be King for the first time since his coronation after he incurs the wrath of the formidable Queen Annis. Arthur has to find the strength to be his own man and become the leader Camelot so desperately needs at the moment.
After Merlin ends up falling into Morgana\'s hands, he becomes an important weapon in her effort for supremacy. Using some ancient magic, she makes friend go up against friend and creates the perfect assassin. Arthur has no clue that he is in great danger.
Morgana joins forces with enigmatic wizard Alator to uncover a secret that could change the course of destiny, as the magical drama continues. With allies on both sides of the castle walls, can anyone stop her before Merlin's greatest secret is revealed?
Merlin is drawn to a distant village when a mysterious illness strikes. However, it soon becomes clear that something sinister turns the air sour and that there is much more at stake than just his own well-being. Far from home and having to fare by himself, Merlin becomes entangled in a deadly game of cat and mouse where he can trust no one.
After Sir Lancelot makes a dramatic return from the dead, old feelings end up being reignited. Gwen findsa herself having to fight temptation before she commits an act of betrayal. Merlin becomes suspicious about Lancelot.
The Camelot Knights discover a strange shrine in the forest. After Elyan ignores Merlin\'s warning, he ends up starting a chain of events more frightening than anyone could have imagined.
Morgana ends up discovering a powerful ally in the Southron warlord Helios and they come up with the perfect plan to bring Camelot to its knees. With Arthur preoccupied by the beautiful Princess Mithian, it ends up falling to an absent friend to raise the alarm.
Morgana is now the head of a vast Southron army and a deadly net is closing around Camelot. After the sorceress strikes everyone is forced to run for their lives including Arthur. It is down to Merlin to try and save Arthur from Morgana's clutches.
Morgana and Helios have managed to take control of Camelot and Merlin and Arthur are now outlaws on the run. After becoming trapped in Ealdor with the army closing in, their situation ends up looking dire. Merlin attempts to restore Arthur's faith before it is too late.