We begin, as we often do, in a forest. Arthur and his men are returning from a trip, and Merlin has a cold. However, something is wrong. There’s smoke, evidence of fighting, and dead bodies.
A hooded figure suddenly runs from the scene, and Mordred gives chase. As she trips over he recognises her, and calls her Kara. Seeking to protect himself and her from intrusive questions he tells her to run on, and tells Arthur that it wasn’t a human, it was a deer. Merlin, who saw the whole thing, is nonplussed.
The next day, Merlin is in a sulk because Mordred can’t be trusted. However even Gaius can’t see his point, and he knows that Merlin talks to dragons. What’s a secret wizard to do?
Mordred, meanwhile, is sneaking around Camelot, poking about in Gaius’s potion stash, and making off with a couple of bottles. That night, he sneaks out, past the reliably slack Camelot security, and uses his mental magic to find Kara in the blackness of night. They hug. Then he sets about mending her leg wound.
Kara asks why Mordred is a knight, and he explains that Arthur is a good man and a friend. But Kara points out that the king doesn’t know he’s a druid, and despite his optimism, this remains his weak spot. Back in Camelot, Merlin challenges Mordred, quite nastily, and Morded explains that Kara is an old friend, a druid too. He begs Merlin to keep the secret, and an accord is struck.
Arthur and Merlin go out on patrol, and Arthur finds a trail, which leads him to Kara (via a deer). Despite Merlin’s best efforts to keep things calm. Kara tries to stab Arthur, a thrust only narrowly diverted by Merlin’s magic. Arthur throws Kara in jail. And now Mordred believes that Merlin betrayed him, and swears revenge.
Kara has her day in court, and refuses to believe Arthur is not as prejudiced against her people as his father. He believes her mind has been poisoned by Morgana, and she insists that she would happily stab Arthur again. Arthur sentences her to death, the following morning, much to Mordred’s horror.
After vowing that he will not let her die, the magical knight rushes to Arthur, explaining that it was he that treated Kara’s wound, and begging for mercy, with tears in his eyes. Arthur will not be budged, forcing Mordred to conclude that his great king is not the man he thought he was.
Mordred decides to act. First he apologises to Arthur for secretly looking after Kara, but his apology sounds like a farewell. Merlin tackles Mordred over his plans, and it’s clear he wants to spirit her away, preferably without spilling anyone’s blood in the process. Mordred stalks off, muttering darkly that Merlin had better keep his secret.
Merlin fears that Mordred and Kara will be picked up by Morgana, and they will somehow kill Arthur, as predicted by the dragon. He decides that the time has come to actually betray Mordred, and goes to see Arthur.
As Mordred and Kara sneak out, Kara brutally murders one of the King’s Guards. They run off into the night, with Mordred’s doubts over the savagery of Kara’s opinions being put aside in their haste to escape the patrols that are now chasing after them.
Arthur catches up with the fleeing pair, slowed by Kara’s injury. Despite his misgivings, Mordred refuses to attack his former friends with magic, and asks Arthur to let them go in peace. This doesn’t seem likely, as as Mordred steps forward to attack the king, he is knocked out by Percival. The pair return to Camelot in chains, and Mordred knows exactly who is to blame: Merlin.
Merlin begs Arthur for mercy for both of them, and although he’s willing to forgive Mordred, he is resolute on the matter of Kara’s sentence, she must die.
The next morning, Kara is taken to see Arthur. He asks her to repent her crimes, and he will save her life. She refuses, telling Arthur he deserves everything that is coming to him. Mordred, still fighting against his better nature, finally gives in to his dark heart, at the exact moment Kara is hanged. He uses his magic to escape, and travels straight to Morgana, intent on betraying the man who did him wrong.
And that’s exactly what he does. He tells Morgana who Emerys is, and where he can be found, setting the stage for Arthur’s final battle.