Camelot has been under siege since Merlin set the Great Dragon free. Merlin is overcome by guilt, but he remains at Arthur's side as the Dragon attacks. Flaming arrows fill the sky, but it's no use. Merlin asks the Dragon why he is doing this. Full of rage the Dragon responds that he will never truly be free after everything has Uther done.
The only man capable of controlling a dragon is a Dragonlord, and Uther wiped them all out in The Great Purge. Or did he? Gaius admits one such man could be still alive. His name is Balinor and he was last seen in Cenred's Kingdom. Arthur volunteers to find him, but the dangers are great - Camelot is at war with Cenred. But what chance there is of finding Balinor is their only hope.
As Merlin packs, Gaius explains - the Dragonlords were men who could talk to the Dragons in their own language. Uther used the Dragonlords to kill or capture the dragons, then executed them for having magic. Gaius admits he helped Balinor escape, and goes on to explain that when Balinor escaped, he went to stay with Gaius' good friend Hunith, Merlin's mother. Balinor is Merlin's father. Merlin and Arthur pass into Cenred's kingdom, with danger all around them. Even more troubling is the wound Arthur sustained in battle. He swears it's not a problem, but Merlin can see it's affecting his riding. Merlin and Arthur arrive at a tavern and start asking questions. Unfortunately, quizzing the locals about Balinor amounts to nothing.
Later, Arthur and Merlin catch a thief. Terrified, the man gives them directions to the last place Balinor was seen, but warns that the hermit will be of no help. They set out again, Arthur's injury worse than ever. Before Merlin can do anything to help, they are forced to hide from foot soldiers. The coast is soon clear, but Arthur has passed out. Merlin leads an unconscious Arthur to a cave at the foot of the Feorre mountain, where Balinor was last spotted. Suddenly, Merlin feels a blade at his throat and hears a gruff voice. Merlin asks for help for his friend, overwhelmed as he turns to look at his father for the first time.
Balinor prepares a poultice and mutters a quiet spell over Arthur's wound. Merlin questions Balinor about his past. He reveals that the Great Dragon is destroying Camelot, but Balinor doesn't care. He knows the Dragon as Kilgharrah and sympathizes with the creature's rage. As far as Balinor is concerned, Camelot can burn.
Arthur wakes, amazed at his recovery and thrilled they have found the Dragonlord. But Merlin is badly disappointed in his father and tells Arthur Balinor will not help them. As the boys prepare to depart, Merlin mentions Gaius, bitterly recalling what he was told about the nobility of the Dragonlords.
Arthur and Merlin head off. There is a sudden noise, and the boys prepare for an attack...but it is Balinor. Merlin's talk of Gaius shamed him - there are people who risked their lives for him, and the debt must be repaid. Merlin's hopes rise as he finally sees something in his father to be proud of.
As Merlin and Balinor collect firewood, Merlin admits that he knows Hunith; she is his mother. Balinor is glad to hear that Hunith is well but hurt that she remarried. Merlin clarifies - she never married. He is Balinor's son. Balinor is thrown, but a gentle smile flickers over his face. Merlin's heart soars.
That night, as Arthur sleeps, Balinor tells Merlin he feared that his presence would endanger Hunith, and he wanted her to be safe. He explains that no man chooses to be a Dragonlord; it is passed down from father to son. In time, Merlin will be a Dragonlord, too. Merlin goes to sleep with happy tears in his eyes. At long last, he has a father.
At dawn, they are set upon by Cenred's men. Arthur's fight takes him into the woods, and suddenly, Merlin is left exposed. A soldier prepares to run him through, but Balinor leaps in to block the death blow. Merlin is saved, but Balinor is mortally wounded. Flooded with anger, Merlin sends out a bolt of magic that slams the soldier into a tree. Merlin falls to his knees and cradles his father's body. Balinor tells Merlin to be strong, and to remember that a dragon's heart is on his right side, not his left. Balinor knows Merlin will do him proud. And then he is gone.
Arthur and Merlin return to a doomed Camelot. Arthur tells his father he will not give up. He will gather his Knights and take the fight to open ground. Merlin is devastated. He couldn't save his father and now there is no one left to tame the Dragon.
In a wide clearing, Arthur, Merlin, and the mounted knights wheel in formation as the Dragon circles above. This time, the men surprise the Dragon - they scatter. The beast is thrown by the new tactic and lands with a crash in the middle of the two arcs. Arthur scrambles to his feet, then twists under the Dragon's body, planting his spear in the ground and using the creature's weight to drive it deep into its side. The Dragon roars with pain but, a second later, a claw smashes Arthur to the ground.
The Dragon limps forward to finish the prince...but then Merlin steps up, terrified. The Dragon tells Merlin he has failed in his destiny. Suddenly, Merlin growls in a language utterly unlike his own - the ancient tongue of the dragons. Kilgharrah shrinks back meekly. The Dragon makes an appeal, begging Merlin not to make him responsible for the death of all Dragonkind. Angry again, Merlin thrusts at the Dragon's heart, but stops, unable to apply the coup de grace. He shouts at the Dragon to go far from Camelot, insisting that the beast show the mercy to others that Merlin has shown him. The Dragon bows his head - he will not forget this clemency.
Merlin watches as the mighty beast takes to the air. Arthur stirs and, together, he and Merlin make their way back to the castle, and to the joy of their people.
Morgana and Mordred prepare to destroy Camelot (and Morgana plots to destroy Emrys). Is Merlin Camelot€™s last hope?
Mordred battles between his duty to his friends and that to his love, but is spared the choice.
Merlin star Colin Morgan talks about the important events from episode 511 'The Drawing of the Dark.'