When Morgana is determined to threaten both Arthur’s future and the balance of the world, Merlin faces his toughest challenge. She summons the mighty Callieach and manages to tear open the veil between the worlds and releasing hellish creatures into the world. It is, up to Arthur to save the world. Merlin too has to come in to restore the equilibrium between the worlds. As Lancelot rushes back to Camelot with a dying Merlin, Arthur has to continue his mission of vanquishing the Dorocha. The power of love changes all their lives forever. Its Arthur’s birthday and everyone is anticipating its celebration. Odin, Arthur’s old adversary promises to make it an unforgettable birthday celebration. A deadly assassin is seen lurking among the birthday party guests, and Merlin has to make a tough decision.

Julius Borden arrives in Camelot with news of a magical secret, which threatens to change the kingdom’s landscape forever. He holds the key to the tomb of Ashkanar, which has the last egg of the dragon. Merlin id determined to help him but asks himself why Julius would be interested in this egg. Since his coronation, Arthur finds out what it genuinely means to be king. He incurs the wrath of Queen Annis as his first challenge. He has to become the leader that Camelot needs desperately. Merlin falls into Morgana’s hands and becomes an extremely deadly weapon. Morgana uses magic to put friends against each other and creates the perfect assassin in Merlin against Arthur.

Merlin is struck by an unusual sickness, and he has to go to a distant village. He is stuck in a game of cat and mouse but is not sure if he is the hunter or the prey. Sir Lancelot returns from the dead, igniting old feelings.