Captured by the Saxons (and a now adult Mordred), Arthur and Merlin seem to be in big trouble. However, Mordred shows them a kindness that Arthur welcomes but Merlin remains suspicious of. Merlin and Arthur manage to escape from the Saxons and head to Morgana's tower. To gain entry, Merlin and Arthur disguise themselves but are soon outed. Merlin tries to save Arthur from Morgana's sword but is incapacitated. Instead, Mordred - who Morgana believed was an ally - saves Arthur.
In Camelot, Sefa is imprisoned by Gwen for betraying Arthur's tactical plans to her dad, Ruadan. Sefa pleads for her life, but Gwen keeps her locked up. Which is actually a ploy on Gwen's part to get Ruadan to Camelot to rescue his daughter, which he does. Ruadan manages to escape with Sefa thanks to his Druid powers, but he is fatally wounded in the process.
With the help of a magical creature, the Diamair (that sort of looks like one of the aliens from Close Encounters of the Third Kind), Merlin, Mordred and Arthur recover Sir Gwaine, Percival and the rest of Camelot's knights. They return to Camelot. Arthur knights Mordred, but Merlin remains suspicious of him. Meanwhile, we see Morgana and her dragon on the move, still plotting.