Storybrooke is about to be inundated with all-kinds of hellish creatures courtesy of Hook (Colin O'Donoghue) in the upcoming episode of the fairy tale drama series "Once Upon a Time."

In the promo released by ABC, viewers can see an army of Dark Ones about to cause chaos in the lives of the characters. At the end of last episode, Dark Hook summoned the creatures from the Underworld using the blood of someone in Rumpelstiltskin (Robert Carlyle), who had gone to Hell and back. He dipped his blood-soaked hook in the pond, which was said to be a portal from hell. Emma (Jennifer Morrison) tried to stop him but she was too late.

With the arrival of the legion of darkness, almost every character will have their life in jeopardy in one form or another. The clip already shows the hooded creatures going after Mary Margaret (Ginnifer Goodwin). Regina (Lana Parrilla) is also seen in the promo, as she stares incomprehensibly in the bedlam the Dark Ones is causing. The army appears to have only one goal — to destroy anyone who dares to go against them. As all in Storybrooke want to fight, they will all be in danger.

Last episode, Hook was so angry with Emma for changing him into a Dark One just like herself. When the Excalibur cut him, Hook was supposed to die. But Emma did everything she could to save him so that they could "live happily ever after." Unfortunately, Hook did not see it her way. He said that after what she did, he only felt hatred for her and that she was "nothing more than a pretty blonde distraction." Hook also told her he would hurt her the way she had hurt him.

Hook then stole the dreamcatchers, which held everyone's memories. Emma needed all the help she could get to stop Hook and to do that, she had to make the characters remember everything. She set out to get the dreamcatchers, but when she eventually found them, it was too late. Hook had already defeated Rumple and got his blood. The last thing viewers saw, he was opening the portal to hell. Will Emma and the rest of Storybrooke be able to keep Hook's minions at bay?

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