Our fugitives are still on the run from Agravaine, but Merlin calls the Great Dragon to help him ward off the troops and buy the party some time. Agravaine discovers Merlin's magical secret, but is dispatched, and ultimately killed, by the young and powerful wizard. Unfortunately, things are not as positive all around, as Arthur is not over his resentment toward Gwen and can't get along with Tristan.
Arthur confides in Merlin that his doubt is getting the better of him. In an effort to restore the king's confidence, Merlin leads Arthur through the forest to a sword in a stone. He claims it was placed there by the first king of Camelot, and that Arthur is special, and can remove it. When he sees his kingly friend is believing in himself, he uses his magic to allow the sword's removal. His vigor returned, Arthur vows to lead his knights in an assault on Morgana's forces.
Back in Camelot, Morgana continues to torment Gwaine and Gaius. Her confidence is shaken both by reports of Agravaine's death and by a burning straw doll Merlin places under her bed while disguised as Emrys. The next morning, she faces a force that, in addition to Arthur and his knights, includes Tristan and Isolde, who have had a change of heart toward the young king upon witnessing his nobility.
And then, battle. Merlin's magic counteracts Morgana's abilities, and Arthur and his knights engage Helios and his forces. Despite dispatching Gwen easily, the sorceress is wounded, and eventually seemingly dispatched by Merlin in a fall of rubble. But when the dust clears, she is gone.
Meanwhile, Arthur's confrontation with Helios seems to be going badly for the boy king, but the Southron warlord is dispatched by Isolde, who gives her life in the process. After the battle, Arthur and Gwen truly reconcile, with Arthur proposing marriage and Gwen taking her rightful place as Queen of Camelot.
In the forest, a wounded and dying Morgana wanders in defeat. She collapses, and appears on her way out, when the white dragon Aithusa appears and heals her. Morgana expresses her gratitude while the dragon flies away.
Mordred finds himself torn between loyalty and love.
Though Merlin is certain Mordred is at heart an enemy, the young knight is determined to prove his trustworthiness to the great Emrys.
In order to protect Merlin and bring harmony to Albion, Finna sacrifices her life rather than fall prisoner to Morgana.