Merlin and Arthur stop off at a local tavern. Their jovial mood is interrupted by the arrival of a thug, Dagr. Arthur breaks the tension by telling Dagr to stand down, and Merlin, being caught up in the bravado of the situation, goads the thug. Dagr smiles as he calls for his men and twenty ruffians pile into the tavern.
All the locals scatter, except for a rough looking man who gets up to stand face to face with Arthur. To everyone's surprise, the man turns on his heels and punches Dagr. A brawl ensues. In the midst of the skirmish, Merlin finds out the stranger is called Gwaine. Dagr bears down on the Prince with his dagger drawn, but Gwaine leaps in and knocks Dagr flying. Arthur gets to his feet to see Gwaine with a dagger protruding from his leg. Merlin and Arthur depart for Camelot, carrying a wounded Gwaine.
Dagr and his partner in crime, Ebor, pay a visit to an old sorcerer in search of two legendary swords known as Stulorne blades. They also acquire two crystals that allow them to take the form of anyone whose blood the crystal touches. Two Knights, Sir Oswald and Sir Ethan, are on their way to Camelot for a friendly tournament. Dagr and Ebor slay them and use their magical crystals to take the forms of the fallen knights.
Merlin is summoned to the local tavern. A very drunk Gwaine has run up a massive bill, which he can't afford to pay. Merlin does the only thing he can and promises that Arthur will pay. He knows the Prince will be mad, but anything's better than a public flogging. As punishment, Arthur forces Merlin and Gwaine to clean the entire army's boots. An arduous task, but it gives them a chance to bond. Merlin is shocked to learn Gwaine's father was a Knight in Caerleon's army. But Gwaine's dad died penniless and, when his mother went to Caerleon for help, she was turned away. He says nobility is not about birthright, but about the way you live your life.
Sir Oswald cajoles Arthur into an impromptu sparring session. Arthur's legendary fighting prowess wins out and leaves Sir Oswald fuming. As Merlin is collecting equipment, he overhears Sir Oswald telling Sir Ethan that in the melee, he will fillet the little brat. Merlin decides to investigate and heads to their chambers. Once inside, he finds the Stulorne blade and, to his horror, realises it is razor sharp.
Merlin wants to warn Arthur, but Gaius cautions him against accusing a Knight without evidence. Merlin, acutely aware of the risks, is determined to get the proof they need. In the dead of night, whilst trying to find evidence, Merlin is drawn to the crystal around a sleeping Sir Oswald's neck. He looks closer and to his horror...Dagr's face is staring back.
Sir Ethan returns, catching Merlin mid-snoop, and he uses the warlock's head for target practice. From nowhere, Gwaine comes to his rescue. Gwaine's fighting skills are unparalleled and he gets the better of the two thugs. Having heard the ruckus, Sir Leon comes rushing in and arrests Gwaine for attacking a noble.
Merlin enlightens Gaius as to the true identity of Sir Oswald and Sir Ethan.
But their conversation is cut short when they see Gwaine on his knees before Uther. Sir Oswald is demanding an execution and Uther is in agreement. Arthur makes a last-ditch plea and tells Uther that Gwaine saved his life. The King takes this onboard and decides not to execute him. Arthur and Merlin are relieved, but Uther is not finished...Gwaine is banished from Camelot.
Merlin is extremely worried. The melee is in the morrow and Gwaine is leaving. Meanwhile, a knight, Sir Derian, is readying himself for the melee. Unexpectedly, he is struck from behind. To our surprise, the mystery attacker is Gwaine, who looks at Sir Derian's armour with an intriguing smile.
The melee gets underway, and Sir Oswald and Sir Ethan make a beeline straight for the Prince. Merlin is just about to use his magic, when a mystery Knight rides to the Prince's aide, using himself as a human shield. Sensing Arthur's desperation, Merlin uses his magic, sending Sir Oswald tumbling off his horse. Arthur's respite is short-lived, as Sir Oswald quickly gets to his feet and Sir Ethan closes in from the other side. Seriously wounded, the mystery Knight drags himself back to his feet and fights back to back with the Prince.
The mystery Knight knocks Sir Ethan's Stulorne blade from his clutches and catches it in his free hand. Merlin looks on with a smile as Gwaine, with Stulorne blade in hand, runs both Sir Oswald and Sir Ethan through. As the two final Knights, Arthur and Gwaine square off. To everyone's amazement, Arthur lays down his weapons, declaring that the Knight defended him with honor. Arthur encourages the Knight to reveal himself and is shocked to find Gwaine beneath the armor.
Realising that Sir Oswald and Sir Ethan are dead, Uther blames Gwaine and calls for his execution. Gaius hastily interjects, ripping off the knights' crystals and revealing them for thugs. Arthur is stunned to see the faces of Dagr and Ebor and realises that once again he owes Gwaine his life.
Merlin is relieved, but the celebrations are short lived as Uther is unwilling to lift the banishment. Merlin is concerned for his new friend and wonders what Gwaine will do next. Gwaine is thinking of Mercia, but Merlin warns him that is a dangerous part of the world. Gwaine smiles; he knows this already.
Merlin has pushed the limits of his strength to save Arthur, but even he may not be powerful enough to rescue Camelot€™s king.
In the battle foretold by the prophecies, all give their best, and Merlin wins the day.
Morgana may have one last trick up her sleeve to win the war.