This season of "Vikings" follows Ragnar Lothbrok, a legendary warrior seeking glory and new lands for his people. His brother, Rollo, desires power and a place in the Frankish kingdom, while Ragnar's wife, Lagertha, fights to maintain her own power and independence. The core conflict revolves around Ragnar's ambition, his family's internal struggles, and the ongoing clashes with other kingdoms.

The season's central conflict escalates as Ragnar faces betrayal from his brother Rollo, who sides with the French, leading to a devastating Viking defeat. Ragnar's health deteriorates due to drug use and injuries, and he eventually abdicates leadership. A major turning point is Ragnar Lothbrok's death by snakes in a pit, orchestrated by King Aelle. This event ignites a fierce desire for revenge among his sons.

The season concludes with Ragnar's sons, united in grief, vowing vengeance. They assemble a massive army, the Great Heathen Army, and launch a brutal invasion of England. This leads to the execution of King Aelle via the blood eagle and a significant victory for the Vikings. However, internal strife among Ragnar's sons surfaces, culminating in Ivar killing his brother Sigurd, fracturing their brotherhood as they stand poised for further conquest.

Season 4 of Vikings covers episodes 1-20. Here's everything that happened:

Season 4, Episode 1: A Good Treason - Ragnar survives his near-death experience, only to face betrayal from his brother Rollo, who massacres his own men to secure his position in Paris. Meanwhile, Bjorn arrests Floki for Athelstan's murder, and Aslaug consults the Seer about succession, hinting at future power struggles. The episode concludes with Rollo solidifying his alliance with the Franks, effectively severing ties with his Viking kin.

Season 4, Episode 2: Kill the Queen - Aethelwulf rescues Queen Kwenthrith from rebel nobles in Mercia, while Ragnar captures a fugitive Floki and punishes him. Bjorn endures the harsh Scandinavian winter alone. The episode concludes with the death of Helga and Floki's daughter, Angrboda, and Ragnar's violent confrontation with Aslaug, effectively ending their marriage.

Season 4, Episode 3: Mercy - Ragnar, guided by a vision of Athelstan, chooses mercy and frees Floki from his brutal torture. Meanwhile, Bjorn proves his survival skills by killing a massive bear during his self-imposed exile. In Hedeby, Kalf plots with Erlendur to assassinate Bjorn, revealing his treachery to Lagertha. The episode concludes with Rollo struggling to adapt to life in Paris and learning French, while Ecbert and Judith's affair deepens.

Season 4, Episode 4: Yol - During the Yule celebration, Ragnar experiments with hallucinogenic drugs with Yidu, leading to a psychedelic episode. Bjorn brutally defeats a berserker assassin sent by Kalf and Erlendur, and then takes Erlendur's wife, Torvi. King Harald Finehair arrives in Kattegat, boldly taking Ragnar's seat, setting the stage for future conflict. The episode concludes with Bjorn and Ragnar returning to Kattegat to find Harald already there.

Season 4, Episode 5: Promised - Ragnar confides his darkest secrets to Yidu, revealing his loss of passion for raiding and his past betrayals. In Hedeby, Lagertha, after announcing her pregnancy to Kalf, stabs and kills him on their wedding day, reclaiming her earldom. Meanwhile, in Wessex, Ecbert supports Kwenthrith's claim to Mercia, while Count Odo faces betrayal in Paris. The episode concludes with Ragnar's growing reliance on Yidu's "medicine" and the arrival of King Harald's brother, Halfdan, in Kattegat.

Season 4, Episode 6: What Might Have Been - Ragnar's drug use and isolation intensify as he leads the raid on Paris. Lagertha confronts Erlendur, and Kalf is confirmed dead after Lagertha fulfills her promise. Meanwhile, Rollo betrays Ragnar by siding with the French, setting the stage for a major confrontation. The episode concludes with the Vikings facing internal divisions and external threats as they approach Paris.

Season 4, Episode 7: The Profit and the Loss - A disastrous river raid on Paris results in heavy Viking casualties, with Rollo's strategic defense leading to a crushing defeat for Ragnar. Upon returning to camp, the Vikings find it destroyed, and Helga is discovered severely injured. Meanwhile, Ragnar rescues a drowning Floki, and in Kattegat, Floki experiences a vision of Aslaug and Harbard.

Season 4, Episode 8: Portage - Ragnar devises a daring plan to bypass Paris's defenses by portaging the Viking longships over land with Floki's engineering genius. Meanwhile, in Wessex, Queen Kwenthrith is murdered by Judith while attempting to kill King Ecbert. Back in the Viking camp, Ragnar drowns Yidu in front of his sons, a brutal act that deeply disturbs them. The episode concludes with the Vikings successfully launching their ships upstream, poised for a renewed assault on Paris.

Season 4, Episode 9: Death All 'Round - The Vikings' arduous land journey with their ships nears Paris, while King Harald and his brother Halfdan engage in brutal acts of violence at a Frankish farm. In Kattegat, young Siggy is found drowned, and Aslaug struggles to maintain control. Meanwhile, Erlendur is killed by Torvi, who then turns the crossbow on him, finally freeing Bjorn from his threat. Lagertha suffers a devastating miscarriage.

Season 4, Episode 10: The Last Ship - The epic battle between Ragnar and Rollo culminates in a brutal, hand-to-hand fight. Rollo emerges victorious, forcing Ragnar's retreat. In Paris, Rollo is hailed as a hero and crowned Caesar. The episode concludes with a time jump of several years, revealing a grown-up Bjorn and Ragnar's continued absence from Kattegat.

Season 4, Episode 11: The Outsider - Ragnar returns to Kattegat after an eight-year absence, finding his sons grown and his kingdom changed. He attempts to reconnect with his sons, Floki, and Lagertha, but they all have their own paths. Ragnar makes a failed suicide attempt, only to be saved by ravens, indicating the gods are not finished with him. He ultimately decides to travel to Wessex to confront King Ecbert, taking his youngest son, Ivar, with him.

Season 4, Episode 12: The Vision - Ragnar and Ivar set sail for England, despite Aslaug's vision of Ivar drowning in a storm. Bjorn also departs on a voyage to the Mediterranean with Harald Finehair and Halfdan the Black. Tensions rise between Lagertha and Aslaug, culminating in Lagertha's vow of retribution. The episode ends with Ragnar and Ivar's ship caught in a violent storm at sea, leaving their fate uncertain.

Season 4, Episode 13: Two Journeys - Ragnar and Ivar, stranded in Wessex after a storm destroys their fleet, brutally murder their remaining men to travel alone to King Ecbert's gates. Meanwhile, Bjorn secures passage to the Mediterranean by forcing Rollo to endure a near-drowning ordeal. The episode concludes with Lagertha launching her assault on Kattegat, initiating a civil war for control of the kingdom.

Season 4, Episode 14: In the Uncertain Hour Before the Morning - Lagertha seizes control of Kattegat by killing Queen Aslaug. Meanwhile, Ragnar, a captive of King Ecbert, negotiates his own demise, agreeing to be handed over to King Ælla in exchange for Ivar's safe return. The episode concludes with Ragnar accepting his fate, acknowledging that his death is inevitable.

Season 4, Episode 15: All His Angels - Ragnar, facing his execution by King Aelle, shares final wisdom with his son Ivar, urging him to seek revenge on Ecbert. Ragnar bravely endures torture and is ultimately killed by snakes in a pit. Ragnar Lothbrok dies, fulfilling his own prophecy of a defiant end. In Kattegat, Ivar learns of both his father's death and his mother Aslaug's murder by Lagertha.

Season 4, Episode 16: Crossings - The sons of Ragnar learn of their father's death through visions and a visit from Odin. Bjorn leads a raid into the Mediterranean, while in Kattegat, Lagertha solidifies her rule amidst challenges from Ivar. Floki experiences a spiritual awakening in a mosque, and Helga adopts an orphaned girl. The episode concludes with Ragnar's sons united in their grief and vowing vengeance for his death.

Season 4, Episode 17: The Great Army - Ragnar's sons begin assembling a massive army to invade England and avenge their father's death. In Kattegat, Ivar and Ubbe attempt a coup against Lagertha, but Bjorn's unexpected return thwarts their efforts. Meanwhile, King Ecbert continues his efforts to educate his grandson Alfred in Wessex. The episode concludes with the Great Army poised for invasion.

Season 4, Episode 18: Revenge - The Great Heathen Army lands in Northumbria, initiating Ragnar's plan for vengeance. Bjorn asserts leadership over his brothers, while King Aelle faces the consequences of his actions. King Aelle is brutally executed via the blood eagle, and the episode concludes with the vast Viking army poised for further conquest.

Season 4, Episode 19: On the Eve - Prince Æthelwulf's army is outmaneuvered by Ivar's strategic brilliance, leading to a devastating defeat. Meanwhile, in Kattegat, Lagertha successfully defends her city against an attack orchestrated by King Harald. Torvi tragically dies during the defense of Kattegat. The episode concludes with the sons of Ragnar poised for victory in Wessex, while King Harald brutally murders the husband of the woman he desires.

Season 4, Episode 20: The Reckoning - Following a devastating battle, King Ecbert abdicates his throne to Aethelwulf and chooses to die by his own hand. Helga is tragically killed by the orphan she adopted. The Viking brothers argue over the future of their conquests, leading to Ivar killing his brother Sigurd. Ecbert's calculated death allows him to die with dignity, while Sigurd's death fractures the brotherhood.