After the wedding, Catrina tells Uther that her father's seal has been stolen by Merlin. Arthur sends his men to find the seal while he rushes to his chambers to warn Merlin, ordering him to leave Camelot for his own safety. Merlin leaves as Arthur tells his father that Merlin has escaped his men and could be out of Camelot.
Underground, Catrina praises her plan of getting Arthur undermined by his father. In the forest, a scrap of Merlin's clothing is found and returned to Camelot with news that Merlin is headed for the northern border. Gwen worries for Merlin's life while Gaius reassures her he can outrun them, before returning to his quarters. Merlin, who had been hiding in a barrel in Gaius' quarters, leaves to follow Catrina.
While spying on her, Merlin witnesses Catrina taking the potion which provides her with the human body. In the throne room, Uther tells Arthur he is imposing a new tax on the poor even though Arthur protests they cannot possibly meet its demands. Catrina says that Uther had been considering such a tax for quite awhile when Arthur mentions the sudden change in his father's attitude to the treatment of the citizens of Camelot. While sleeping, Merlin sneaks into Jonas' room and steals the potion and takes it to Gaius. Merlin asks Gaius to replace the potion with a similar one which would reveal Catrina's true form, and they set about making it before Jonas awakes in the morning.
Still enchanted, Uther continues to make romantic advances toward Catrina, who continues to rebuff him. Catrina questions his ability as a man and a king, stating that Arthur is not fit to take over. She states that Uther's love for Arthur blinds his decisions and that he cannot be trusted. The following morning, Gaius presents Merlin with the replacement potion to take back to Jonas' room. As he does so, Merlin is forced to hide as Jonas returns unexpectedly.
In the city, Arthur comes across a man who has been apprehended for not being able to pay the king's tax. As Gwen watches on, Arthur releases the man and orders his men to give everybody's money back. In the castle, Catrina and Uther chastise Arthur on his decision and Arthur simply states he thinks his father is wrong by assuming that royalty and the people cannot be equal. Uther demands that Arthur return into the town to collect the payments, but Arthur stands his ground and refuses to do so. Catrina states that the people of Camelot would not respect her unless she was the heir to the throne, prompting Uther to agree to the request.
Catrina returns to Jonas' room for her next dose of the potion. As she takes it, Catrina and Jonas leave the room, allowing Merlin to emerge from his hiding spot relieved. In his chamber, Gwen visits Arthur to commend him on his actions in the town earlier that day. Arthur laments that Uther now hates him and that the tax will still be imposed, but Gwen states that the people will always remember Arthur's clemency. Arthur says that maybe Uther was right in saying he could not be both a king and a friend to the people of Camelot, but Gwen firmly tells him that he has a kind heart and that he should not change for anybody.
After being summoned to Uther, Arthur's title is revoked and is disinherited for opposing him. Arthur states that he only acted as he was brought up to act but Uther stands firm, sending Arthur away in shock. Catrina is named as the rightful heir to the throne, much to everyone's shock and confused applause. Merlin rushes to deliver the news that Catrina had taken the replacement potion to Gaius, only to be met with the news of her inheritance to the throne. At the Catrina's ceremony, Merlin watches on from above as she takes her oath. As she does so, her troll form begins to emerge. Catrina snatches the crown and runs from the room to avoid being caught out, only to be pursued by Uther, Morgana and Arthur. Merlin uses his magic to lock the doors and as she tries to open the door, Catrina reverts back to her true self.
Still under the influence of the pendant, Uther is appalled when Arthur reacts disgustedly to the revelation of Catrina's true form. As Arthur tries to convince his father of the sight of his wife, Catrina yanks the door off its hinges and runs away, Uther on her heels. In their chambers, Uther apologises to Catrina, still remaining affectionate. The next morning, Gaius goes to Uther in the council rooms to confront him about Catrina. Uther remains oblivious to the fact that his wife is a troll and states that the next person to insult his queen will be tried with treason and beheaded. Gaius advises Merlin to go to the Dragon for advice as troll magic is very powerful to overcome: however, he advises Merlin to be careful, as the races of dragons and trolls have long been allies.
After hearing of the story from Merlin, the Dragon laughs uproariously at the thought of Uther marrying a troll. The Dragon says that the only way to break the enchantment is if Uther cries true tears of remorse: he also warns Merlin his advice doesn't come without a price, and reminds him of the promise he made to free the Dragon. Merlin goes to Arthur with the proposal that if he fakes his own death, Uther will be so affected that he will cry tears of remorse. Once Arthur has taken the potion and appears to be dead, Gaius leaves to tell Uther while Merlin is attacked by Jonas; causing the bottle containing Arthur's antidote to smash.
While Uther cries for Arthur, Catrina tries to lure him away as Merlin mops up the remains of the antidote. Uther, with the enchantment broken, sees Catrina for her true self and becomes disgusted. As Catrina takes on the guards, Merlin revives Arthur and he is knocked unconscious after trying to stop her. Jonas tries to kill Arthur and in turn is killed himself. Arthur, with the help of Merlin's magic, kills Catrina.
Following the night's events, Uther thanks Arthur for exposing him to Catrina though blames it on magic once again and they laugh over the events. Arthur thanks Merlin for his help and they share an awkward moment of mutual gratitude.