Klaus (Joseph Morgan) and Marcel (Charles Michael Davis) are brought together by the Hollow to fight for survival. Meanwhile, Keelin (Christina Moses) might be developing feelings for Freya (Riley Voelkel).

On the next episode of "The Originals" season 4, titled "I Hear You Knocking," Klaus and Marcel are being haunted by the evil entity known as The Hollow, which appears to have become a parasite in their minds.

"Klaus and Marcel experience the symptoms of a malevolent haunting, forcing the two adversaries on a violent collision course. Meanwhile, Hayley (Phoebe Tonkin) and Elijah (Daniel Gillies) head out to speak with Mary (guest star Debra Mooney) after Hayley uncovers a mysterious link between the dark magic and her former wolf pack. Finally, as an exhausted Freya risks her own life to cure Klaus' infection, a guilt-ridden Keelin must decide whether to honor her hypocratic oath and help Freya - or flee the Mikaelson's forever," the episode listing on The Futon Critic reads.

As seen from the episode 5 promo, both Klaus and Marcel experience apparitions of an unknown being, which has led them to a secluded cabin where they will be forced to fight each other for survival.

Meanwhile, Keelin might be developing strong emotions for Freya.

Previously on "The Originals" season 4, Freya agreed to free Keelin as long as Keelin helps her heal Marcel. Keelin accepted Freya's offer, and it appeared that there is tension between the two.

However, executive producer Michael Narducci revealed to E! News that the story of Keelin and Freya will revolve around how Keelin is willing to make this "deal with the devil."

In the upcoming episode, Keelin will also have a chance to escape from Freya, and it is yet to be revealed whether she will grab that opportunity or not.

"The Originals" season 4 airs every Friday night at 8 p.m. EDT on The CW.