To put the Excalibur back together, Emma Swan (Jennifer Morrison) will send for one of the darkest beings known to mankind in the upcoming episode of the ABC series "Once Upon A Time."

In "Nimue," Comicbook reports that the new Dark One will summon a force more terrifying than she will ever be. Emma will reportedly do this to "forge the ultimate weapon." Last episode, she successfully managed to turn Gold (Robert Carlyle) into a hero. He succeeded in extracting the Excalibur from the stone. Before he did, however, he asked Emma to return Merida's (Amy Manson) heart so she could not control her any longer.

Now that she has the sword, Emma will stop at nothing to create the strongest weapon of all. To do that, she needs the spark from mankind's original fire and someone powerful enough to make it work. In the promo released by ABC, Emma can be seen reading a name on her dagger, as she summons the force she herself fears. When she looks around, she is terrified to see a black-clad person with a frightening mask. Who is this being that can scare even the Dark One?

Meanwhile, iDigital Times reports that the term "Nimue" refers to the Lady of the Lake. According to folklore, she was the one who gave King Arthur the Excalibur. Nimue was also responsible for raising Lancelot (Sinqua Walls) and trapping Merlin (Elliot Knight) in the tree. Last episode, Henry (Jared Gilmore) learned from Merlin's note that only Nimue could defeat the Dark One. But before he could hear the rest of the instructions on what they need to do, Emma arrived.

Also in episode 6, viewers saw Merida finally reunited with her brothers. She kidnapped Belle (Emilie de Ravin) so she could make a potion powerful enough to turn her into a bear. Merida wanted to defeat the clans who wanted to marry her and reign over her kingdom with her animal strength. Belle cautioned her in the transformation, but Merida was desperate as she saw on the witch's cauldron that her brothers would be executed.

When she faced the clans, however, Merida did not turn into a bear. Belle substituted the potion with water and told her she needed to defeat them using her bow. When three of the leaders of the clans shot arrows at her brothers, her own weapon sliced through each one, saving her siblings' life. The people were amazed with her skills, and they kneeled to their queen.

"Once Upon A Time" airs Sundays at 8 p.m. EST on ABC.