Morgana finds a powerful ally in the Southron warlord Helios. Together they hatch the perfect plan to force Camelot to its knees.With the kingdom - and Arthur - preoccupied by the arrival of the beautiful Princess Mithian, it falls to an absent friend to raise the alarm: Guinevere.But with past wounds still raw, can love really conquer all? Or is a deadly arrow destined to fly straight into the heart of Camelot?
Exiled and downtrodden, Gwen is shoveling hay when her village is raided by the horse-borne Southrons and their charming, deadly warlord, Helios, who takes a liking to the lovely maiden and takes her for his own. Meanwhile, Arthur is set on marrying the princess of a neighboring kingdom in an effort to establish peace. Merlin protests, but Arthur is determined to make Princess Mithian his wife. As he feasts his betrothed, Agravaine makes off with siege plans stolen from Camelot, which he delivers to Morgana.
Back at the Southron camp, Helios meets with Morgana, who is his old friend. She tells the Southron warrior of her plan to destroy Camelot and of Agravaine's involvement; details that are overheard by a skulking Gwen! The banished maiden flees in an effort to warn Arthur of the danger closing in on him, and is pursued by a furious Morgana. Cornered, the heroine tries to escape, only to be trapped by the evil sorceress and transformed into a deer.
In the same forest, Arthur, Mithian and Merlin are out hunting. Spotting a deer, they pursue it, only for Merlin to realize that the deer is, in fact, the enchanted Gwen! Subtly using his magic, he is able to avert one shot, but eventually, the deer is wounded and vanished. Returning to the forest in the middle of the night, Merlin finds a wounded Gwen and heals her with his magic. Happy to see her old friend, she spills the details of Morgana's plan and the impending Southron invasion.
Since Gwen is afeared to be seen in Camelot, Merlin goes to report her news to Arthur, only to be thwarted once again by Agravaine's treachery and threatened with banishment. But Arthur's bluster hides the fact that he has rediscovered his love of Gwen, and he later confides that fact in Merlin. Merlin encourages Arthur to follow his heart, and we find that the king is capable of doing so when we see Mithian departing Camelot the next morning.
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.'