Ragnar (Travis Fimmel) better watch his back because according to a fresh, Season 4 promo video for “Vikings,” several of the king’s enemies want to sick a knife in it.

In the new trailer for the History Channel series, audiences watch as Erlendur (Edvin Endre) proposes a plan to Earl Kalf (Ben Robson) — one that reveals his true motive for remaining in Hedeby.

“I thought we came together to destroy the family of Ragnar Lothbrok,” the son of the late King Horik (Donal Logue) says. In the Season 2 finale of “Vikings,” the King of Denmark was killed after his failed attempt to take down Ragnar and his family. Now Erlendur, who was spared by Ragnar, will attempt to avenge his father’s death by finishing King Horik’s scheme of taking out the Lothbrok clan — starting with Bjorn (Alexander Ludwig).

The promo video shows Bjorn going head-to-head with a gruesome warrior in the middle of the snow-covered, Scandinavian woods in a forthcoming episode. The synopsis for episode 3 reveals that it was Kalf’s idea to send the assassin.

But like Bjorn, someone is also coming for Ragnar’s head. In a sneak-peek clip, it’s unveiled that a newcomer will arrive to Kattegat with the dream of becoming king.

“To become king of all Norway you would have to overthrow my husband,” Queen Aslaug (Alyssa Sutherland) says with intrigue. Could the queen be aiding her husband’s enemy with the hopes of taking Ragnar down for her own benefit? After all, she admitted in the Season 4 premiere that she's eyeing the throne for herself.

Sound off in the comments section below with your thoughts. “Vikings” airs Thursdays at 10 p.m. EST on the History Channel.