This review contains spoilers! Proceed with caution.

‘Nimue’ went a long way back in time to show us the origin of Merlin’s powers. The subsequent love story between he and the episode’s titular character was a mirror for Emma and Killian. By depicting both sides of the same coin, Once Upon a Time highlighted the perils of being in love with the Dark One.

This episode was a look at the man behind the mystery. We glimpsed Merlin’s relationship with Nimue – the love of his life – through numerous flashbacks. Although Merlin was willing to give up his immortality to grow old with her, it was ultimately Nimue’s desire for revenge that drove them apart. Much like Rumplestiltskin, she became the Dark One to obtain power. The scene where Emma summoned her was my favourite this episode, mostly due to Elliot Knight’s superb acting. It was obvious from the way Merlin could barely look at her that he is still mourning her ‘death’. I found it fascinating that Merlin embodies light magic while Nimue is the very essence of darkness. It gave them an intriguing yin-and-yang vibe that I’d like to see more of. She and Merlin evidently have unresolved feelings for each other, though I’m not sure how reconciliation is possible when Nimue is technically a part of Emma. Even so, fingers crossed that there’ll be more interaction between them in the future.

Merlin and Nimue’s relationship was clearly set up to be a parallel for Captain Swan. Like Merlin, Killian makes a clear distinction between the darkness and the one he loves. This separation is something we haven’t seen before. Belle grew to love Rumple after he became the Dark One, while Hook loved Emma before her transformation. Emma telling Nimue “you killed the woman [Merlin] loved because you killed the woman you used to be” really stuck with me. We’ve seen that Killian has a similar line of reasoning. He remains adamant that Dark!Emma is not the same person he fell in love with. However, things aren’t as black-and-white as that. Emma has insisted time and again that she is still herself, and I agree with that to an extent. The darkness has simply brought out characteristics in her that were previously dormant. It’s certainly added an element of complexity to her and Hook’s relationship, but I don’t buy for a second that he no longer loves her. Despite the parallels to Merlin and Nimue, I’m confident that Emma and Killian’s story will have a happier ending.

Though I liked seeing Merlin’s backstory, the episode was a little lacklustre. There wasn’t enough shown of he and Nimue’s relationship to really become invested in it. I also think that more time could have been dedicated to Nimue’s descent into evil to really emphasise the heartbreak of the situation. The plotline about the Charmings et al. attempting to steal Excalibur used up valuable screen time, and could have been explored more fully in the next episode rather than this week’s. That being said, next week’s two-episode special looks promising and chock full of drama!