The next episode of ABC's Once Upon a Time will be a big one for Merlin (Elliot Knight) as we learn more about his romantic, magical past.

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ABC has released a plot synopsis for the next episode of Once Upon a Time, which is titled Nimue. In this episode, Merlin helps orchestrate a mission to take the dagger and reunite it with Excalibur.

The synopsis continues:

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"With Zelena [Rebecca Mader] in tow, Hook [Colin O'Donoghue], Mary Margaret [Ginnifer Goodwin], David [Josh Dallas], Regina [Lana Parrilla] and Robin [Sean Maguire] steal into Arthur's [Liam Garrigan] castle to take the broken sword from the maniacal king. Meanwhile, Merlin brings Emma [Jennifer Morrison] along on a journey to confront his ancient nemesis and retrieve the sacred spark he'll need to reforge Excalibur. Both parties are tested, but one suffers a blow that could derail the entire operation.

"In a flashback to long before the Age of Arthur, young Merlin finds purpose after he is blessed with magic and immortality, but when he falls in love with a young refugee named Nimue, everything changes for Merlin, as their romance starts a chain of events that touches every one of our present day heroes."

The ABC preview for the new episode focuses heavily on Emma, with Merlin telling her, "the spark from mankind's original fire, that's what we'll need to put it back together," referring to the dagger with the rest of the weapon. The clip shows Emma facing off against a villainous looking hooded creature. Is this Nimue? Only time will tell.

Once Upon a Time airs Sundays at 8 p.m. ET/PT on ABC.

Tags: Once Upon A Time television ABC