Ragnar (Travis Fimmel) better watch his back because according to the Season 4 synopsis of History Channel’s “Vikings,” several power-hungry men will want to stick a knife in it — including his very own brother Rollo (Clive Standen.)

“Betrayal is in the air at the Court in Paris,” the summary reveals, teasing that Rollo will deceive his brother once again in episode 5, titled “Promise."

“When my brother returns, everything will be decided here,” Rollo says, proving that he’s no longer hidden in Ragnar’s shadow.

But the Frankish warrior won’t be the only treacherous character looking to take down Ragnar and his band of vicious Vikings. The Kattegat newcomer, King Harald Finehair ( Peter Franzen ), revealed in episode 4 that he’s looking to win the heart of a princess by becoming the new ruler of Norway.

“But in order to become king of all Norway you would have to overthrow my husband,” Aslaug (Jessica Sutherland) said with intrigue. She too wants the throne for herself. In the Season 4 premiere of “Vikings,” Aslaug asked the Seer (John Kavanagh) if he could one day see a woman ruling Kattegat.

“Yes, I have seen it. A woman will one day rule Kattegat,” he answered without divulging whether that woman would be Aslaug.

With so many foes surrounding him, Ragnar will turn to the only person he can trust — Yidu (Dianne Doan). He will confide in his new friend during episode 5, unveiling his “his deepest secret.”

The summary adds that a “pregnancy will bring happiness to Lagertha (Katheryn Winnick) and Kalf (Ben Robson)” in the forthcoming installment. Kalf had previously told Lagertha that he loved her and wanted to have a family with her — something Lagertha seemed reluctant about when the words “child” left his lips. But even if Lagertha is pregnant, a swollen belly won’t prevent this shieldmaiden from swinging her sword. Audiences can expect Lagertha and her fellow female warriors to clash weapons with an enemy in episode 5.

“Vikings” airs Thursdays at 10 p.m. EDT on the History Channel.