"Vikings" Season 4 spoilers
Bjorn (Alexander Ludwig) returns from his wild adventure in the woods in Season 4, episode 4, of "Vikings." History Channel

Ragnar (Travis Fimmel) is torn. In the opening scene of the Season 4, episode 4, of "Vikings," titled “Yol,” the king of Norway reveals that he’s constantly teetering between thoughts of killing himself or everyone around him. He divulges this intimate information to his slave Yidu (Dianne Doan) in the History Channel series.

“I’m a slave,” she replies, revealing that she too shares similar feelings. Ragnar isn’t entirely surprised by her confession. He notes that it’s both their duties to serve others — “whether we like it or not,” he says as Aslaug (Jessica Sutherland) watches the two from a distance.

Meanwhile in Wessex, King Ecbert (Linus Roache) and his friends celebrate Advent. But the feast turns sour when King Aelle of Northumbria (Ivan Kaye) questions what Queen Kwenthrith’s (Amy Bailey) regal title will mean for her son Magnus — the son of the great Ragnar Lothbrok.

“I once swore an oath before God and all his angels that one day I would kill Ragnar Lothbrok in revenge for his unprovoked and merciless attack upon my kingdom,” King Aelle says, implying the thought of Ragnar’s son ruling a kingdom sends shivers up his spine.

“And would you kill his bastard son as well?” Queen Kwenthrith fires back.

Kwenthrith isn’t the only one feeling protective over her boy. During the Vikings' celebration of Christmas, Ragnar encourages Ivar (James Quinn Markey) to join in the festivities by hanging mistletoe. But when Ivar refuses, his mother runs to his rescue.

“He’s different. You can’t make him what you want. You can’t make him like you. … He’s not you,” the queen snarls, grabbing her son from Ragnar.

As the Christmas celebrations continue, Floki (Gustaf Skarsgård), who has been exiled from the traditional burning of the yule log, pays the all-knowing Seer (John Kavanagh) a visit.

“So, you finally came. I’ve waited a long time,” the oracle says, revealing that he’s waited in the “wet ground between life and death” for hundreds of years. “Don’t play games. I’ve waited and I understand. Show me that you understand. Show me who you are.” (Is the Seer insinuating that Floki is a god? We always thought Floki shared similarities with the trickster god Loki.)

In Frankia, Princess Gisla (Morgane Polanski) takes another step closer toward annulling her marriage with Rollo (Clive Standen). But the Northman begs her to not to divorce him — in her own tongue!

“Princess Gisla, I beg you not to do this. I know my destiny is to be with you and I swear that like you I am prepared to defend Paris to the death,” he says in French. But she’s not entirely convinced that Rollo is devoted to Frankia — that is, until he gives her an item that's most precious to him.

Back in Kattegat, Aslaug proposes to Ragnar that he’s free to “spend some time” with Yidu, revealing that she saw the two bonding in the bath. “You’re free to go with her. I won’t be jealous,” she adds.

So Ragnar obliges and spends time with his slave to learn of her past. Yidu reveals she was captured by pirates on the sea while sailing with her family. She was then sold to the Franks before ending up in Kattegat.

Ragnar then brings her to his secret hideout — a place where he “never feels alone.”

“If you want, you come and go as you please,” he says to her. But she’s skeptical of his offer.

Yidu shares a drug with Ragnar, which he’s reluctant to take at first. So, she swallows it to gain his trust before he gobbles it down. They then sink into a psychedelic trance, which results in Ragnar swallowing a live snake while Yidu crushes up more concoctions.

Meanwhile, in the woods, Bjorn (Alexander Ludwig) hears the crackling of twigs. He’s surprised by a Berserker — the same one who was hired by Kalf (Ben Robson) to assassinate Bjorn and take down the Lothbrok clan. But the killer is no match for Bjorn Ironside, who wraps his enemy around the trunk of a tree with hooks.

“Who sent you?” Bjorn calmly says as he twirls the Berserker’s ring, which Erlendur (Edvin Endre) gave to the killer for protection, in his hand. When the assassin refuses to tell him, Bjorn jabs his knife into his foe, ripping out his enemy's intestines.

As Ragnar bonds with Yidu, Aslaug visits Floki and tasks him with teaching her son the deep and ancient ways of the Vikings. She fears that her son might embrace the Christian faith as her husband does. Floki agrees to this plan, which we can imagine will only strain his relationship with Ragnar even more.

Bjorn returns to Hedeby after surviving the attack.

“We must celebrate your arrival,” Kalf says with false good cheer as Bjorn bursts through the door. But Bjorn says celebrations aren’t necessary … after all, he’s there for business.

“I have come for two reason: First, to see my mother. Second, to take Torvi (Georgia Hirst) with me back to Kattegat,” Bjorn says. Although Torvi is delighted by the news, Erlender is anything but pleased to hear that his wife wants to run off with his foe. So, he makes Torvi's decision to leave even more difficult by telling her their son will stay behind.

“If you want to go with my son, then go with my son. I will look after your child,” Lagertha (Katheryn Winnick) promises. “We have one life, Torvi. So go and live it.”

And Torvi isn’t the only one celebrating her independence. Judith (Jenni Jacques) reveals to her father that like him, she is also free. “You don’t own me, father,” she tells him when he calls her out for being a bad mother and wife, “nor does any man own me. I am free.”

The episode ends with Kattegat receiving a visit from a newcomer — a regal newcomer named King Harald.

According to the king, he’s made the trek to Kattegat to meet the famous Ragnar and discuss his famous raids. During his stay, Harald wins over Ragnar’s sons by playing a game with them and piques Aslaug’s interest when he reveals his true intentions for washing up on their shores.

“I made someone a promise — a girl. A princess,” he clarifies. “I wanted to marry her, but she turned me down. I wasn’t important enough; she had other offers. I decided I had to be worthy of her by making myself the king of all Norway. Then she would have to marry me for sure.”

Bjorn walks in during Harald admission and quickly senses something is wrong.

“But in order to become king of all Norway you would have to overthrow my husband,” Aslaug tells Harald.

Just then, Ragnar enters the Great Hall and welcomes his son.

“Well, look who is back alive and well,” he says before noticing a stranger is sitting in his throne. “And you are?” he asks Harald.

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