Hook (Colin O'Donoghue) and Emma's (Jennifer Morrison) engagement is put to the test, while Regina (Lana Parrilla) fights her alter ego, the Evil Queen (also played by Parrilla), in the upcoming episode of ABC's "Once upon a Time" season 6.

Titled "Page 23," tomorrow's episode will see Rose McIver reprise her role as Tinker Bell. According to the official synopsis, the Evil Queen sets out on a mission to eliminate her other half. She believes there is not enough room in Storybrooke for her and Regina; she uses Robin (Sean Maguire) as bait. Determined to make his relationship with Emma work, Hook seeks advice from his old pal Capt. Nemo (Faran Tahir). Gideon (Giles Matthey) unfortunately messes up Hook's plan before he could even set things right. Meanwhile, a flashback to the Enchanted Forest will see the Evil Queen learn an unexpected lesson about the real source of her unhappiness.

In a new promo released by ABC, the episode opens with the Evil Queen asking Snow White's (Ginnifer Goodwin) whereabouts. Regina faces the Evil Queen and declares, "Our fight ends today." The two engage in a swordfight before the Evil Queen uses her power to throw Regina to the other side of the room. "Let's finish this," the female villain tells her doppelgänger with a sneer.

Parrilla recently caught up with Entertainment Weekly and she offered some teasers about the huge confrontation between the two characters. The actress stated that viewers should not miss the episode because it will feature an epic fight. "It's their final showdown," Parrilla hinted. "It's like b--ch versus b--ch; it's a b--ch battle. They really come toe-to-toe and have a full-on heart-to-heart, but expressed through a lot of built up anger and resentment."

Tinker Bell will also have a moment with the Evil Queen during the flashback. "Tink actually comes back, and confronts the Evil Queen, and says, 'How come you never walked through that Tavern?'" Parrilla added.

The sixth season of "Once Upon a Time" airs every Sunday at 8 p.m. EDT on ABC.