En route to visit her father's grave, Morgana's party is set upon by bandits. After a messy battle her knights are killed and she and Gwen are taken captive. Thanks to Morgana's cunning, they manage to escape Kendrick's clutches...but not for long. When the bandits give chase, Gwen is recaptured and forced to pose as Morgana.
Uther is hugely relieved to have Morgana home safe, but refuses to pay a ransom or send a rescue party for Gwen, a mere servant. Morgana appeals to Arthur, but he shocks everyone by agreeing with his father - they cannot risk the lives of any more knights. Later, in private, he assures Morgana that he's going after Gwen; he just can't afford to publicly clash with Uther.
Meanwhile, Gwen is brought before Hengist, the bandit leader. He makes it clear if Uther doesn't pay her ransom in time, he will have no hesitation in taking her life. Gwen is forced to attend a feast with rough mercenaries and raucous wenches. There's an empty cage in the middle of the room, with a grill-like gate leading into a dark tunnel. Hengist introduces his "champion", a huge ogre of a man, and the new challenger. Gwen reacts with astonishment - it's Lancelot! Gwen watches, heart in mouth, as Lancelot prevails in a closely fought contest.
That night, Merlin and Arthur forge through enemy territory. Merlin's exhausted, struggling to keep up with Arthur's relentless pace. He begs for a rest, but Arthur's having none of it. Gwen's in mortal danger - they cannot rest until she's safe.
Lancelot finds a way to communicate with Gwen through a grill in the wall of her cell. He's ashamed she has seen him in this sorry state. He has abandoned his impossible dream of becoming a knight and now survives by fighting. Gwen's saddened by Lancelot's loss of faith in himself. She can still see hope inside him that belies his words. Stirred by Gwen's faith, Lancelot admits he has never stopped thinking of her. Gwen's moved, but hesitant to articulate her own feelings.
The next morning, steadfast Arthur heads off again before dawn. Merlin marvels - he's never seen Arthur like this about anyone before. Defensive, Arthur claims to not know what Merlin's talking about but the strength of his denial speaks volumes - he's clearly in love with Gwen.
Arthur and Merlin reach the mountains that separate them from Gwen. Arthur decides the quickest course of action is to go underground, through tunnels reputedly infested with wilddeoren. Merlin balks but Arthur smears himself with foul-smelling gaja berries and orders Merlin to do the same. The smell is the only thing that might save them from detection by the blind monsters. It isn't long before his theory is tested. Creeping through the dark tunnels, they meet with a wilddeoren. It gets right up into Merlin's face but he holds still and the creature smells only the berries - it moves off and Merlin is spared.
Lancelot visits Gwen in her cell again. She's sure she'll be dead by tomorrow but Lancelot swears he will get her out, even at the expense of his own life. And why not? For all his grand beliefs and words the last time they met, he has come to nothing. Gwen won't hear such talk - to her, Lancelot is everything that is right with the world. Lancelot's thrown; Gwen's love for him is writ plain. Gwen admits she didn't know she felt this way about him until he had left Camelot. Deeply moved, he declares that he now has reason to live and hope again.
When they are safely out of the tunnels, Arthur apologises to Merlin for risking his life. Merlin's philosophical - love makes people do crazy things. Arthur bristles, denying he feels that way about Gwen. Merlin presses and Arthur admits it's true but insists there's no hope for him and Gwen so there is no point talking about it.
Just as Lancelot poisons the guards outside Gwen's cell and breaks her free, Hengist gets the truth out of Kendrick about Morgana's maid. Lancelot and Gwen make it into the tunnels, but soon hear guards behind them. Lancelot orders Gwen on ahead while he holds them off. Gwen refuses to leave him but Lancelot's firm. He would die for Gwen a hundred times over and begs her to run for her life - and for him. Emotional, Gwen kisses Lancelot and promises her feelings for him will never change. She runs to freedom as Lancelot bravely dispatches guard after guard.
Arthur and Merlin scale the walls of Hengist's castle, overcoming a pair of guards to breach the heart of the castle. Meanwhile, a battered and bruised Lancelot is recaptured and thrown into the cage. Lancelot prepares to die fighting, calm in the knowledge that Gwen has survived. But it's not to be - recaptured, Gwen is tied up with Lancelot in the cage. Hengist releases the wilddeoren and the crowd cheer. Gwen grips Lancelot's hand as they prepare to die together. Just then, Arthur and Merlin arrive. The prince jumps into the cage and, sword drawn, immediately cuts them free. Though stunned to see each other, Athur and Lancelot fight off the wilddeoren together. It looks hopeless until Merlin uses magic to send a huge candelabrum down on the bandits' heads, and opens up the gate leading to the tunnels. Together, he, Arthur, Gwen and Lancelot escape down the passageway.
Once safely out of the tunnels, Arthur and Merlin can't miss the dynamic between Gwen and Lancelot. Lancelot asks Arthur where all the other knights are. Arthur is forced to explain that his father wouldn't permit an official rescue mission. He tries to cover, insisting that Morgana begged him to come, but it's too late - Lancelot now knows that Arthur would risk his life for Gwen.
Staying awake to keep watch, Lancelot quizzes Merlin about Arthur's feelings for Gwen. Merlin tries to be vague in his response but Lancelot reads between the lines - he has his answer, and he knows what he must do. Heartbroken, but as brave and noble as ever, Lancelot departs without a goodbye. He will not come between Gwen and the future King.
Gwen is devastated, especially when Merlin gives her Lancelot's message: She has changed him forever, but some things cannot be. Arthur sees Gwen's pain. It hurts him but he doesn't know how to deal with it. Silent, he leads them home.
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.