Zelena (Rebecca Mader) is out to settle scores with the Dark Swan (Jennifer Morrison) in the upcoming episode of the ABC series "Once Upon a Time."

In her desire to save Captain Hook (Colin O'Donoghue), Emma resorted in all sorts of deceit the entire season. One of her victims was the witch, as the latter was crucial to her plans to get rid of the darkness inside both of them. Emma's plan was to turn Zelena into the new vessel of darkness and defeat her with light magic. In doing so, she extinguished Zelena and dark magic in one sweep.

But Hook was against Emma's plans, and at the end, he was reason why Zelena managed to escape. Now that she is on the loose, Zelena is sure to target Emma, more so when she learns that the latter's only love is angry at her for what she did. Hook could not accept that Emma turned him into a Dark One, just like herself. Regina (Lana Parrilla) has likewise warned Snow White (Ginnifer Goodwin) and Prince Charming (Josh Dallas) that Emma would be crossing the line once she hurt her sister.

Meanwhile, the official promo of "Broken Heart" shows Hook struggling with his new identity as the other Dark One. The pirate also appears to be acquiring a taste for revenge, as all his hate for Rumple (Robert Carlyle) resurface. In the clip, he is seen giving Rumpel a sword and taunts him to finish what they started. The next scene shows the two locked in a fierce battle. Viewers also see him telling Emma that he wants to hurt her in the same exact way that she hurt him.

Executive producer Edward Kitsis explained to Entertainment Weekly Hook's reason for hating what happened to him. He also shared how this turn of events would affect his relationship with Emma.

"The thing he hates most in the world is the Dark One. Rumple took away everything from him and now Emma turned him into the one thing that he hates... All of that is going to play out and it's really going to test their relationship and their love," he said.

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