In the upcoming Winter Finale of ABC’s “Once Upon a Time,” the dark ones are closing in and Hook (Colin O'Donoghue) prepares to exact centuries worth of revenge.

A teaser for Episode 11 of Season 5, titled "Swan Song," shows the hooded dark ones closing in on the streets of Storybrooke to spread their terror.

Talking to his one-time lover Emma (Jennifer Morrison), Hook warns her of the mayhem to come.

“You get to watch everyone you love die,” he says. To which Emma responds, “I will protect my family, even if I have to kill you to do it.”

Hook's plans are intense and include getting revenge on Rumpelstiltskin (Robert Carlyle), as well as sending everyone in Storybrooke, the fairytale suburban setting of “Once Upon a Time,” down to the underworld.

Speaking to The Hollywood Reporter, O'Donoghue talks about how far Hook is willing to go to carry out his dark plans. “His thing is revenge on Rumple, and he’s willing to let the darkness use him in whatever way it needs to get that done,” he said. “Transporting everyone into the underworld through that portal is his way of getting revenge on Rumple.”

According to the 34-year-old Irish actor, Hook is enveloped in darkness and is now willing to do whatever he must in order to make his plans a reality. This includes hurting Emma, who he would rather not kill. “So he’s more of a pissed off boyfriend than wanting Emma to die in any kind of way,” explains O'Donoghue, adding, “But at this stage, he’s just so angry, and when the Dark One gets angry, you do insane things."

The Winter Finale of “Once Upon a Time” airs Sunday, Dec. 6 on ABC at 8/7c.