Ragnar Lothbrok, a Viking leader, seeks new lands for his people. He allies with Princess Kwenthrith of Mercia, fighting her uncle to secure farmland in Wessex. Ragnar's loyal friend, Athelstan, a former monk, aids him. Meanwhile, Ragnar's wife, Lagertha, leads the settlers in Wessex.

The core conflict revolves around Ragnar's ambition and the treacherous politics of England and Mercia. Key turning points include the slaughter of the Viking settlement in Wessex by King Ecbert, and the brutal murder of Athelstan by a religiously zealous Floki. Ragnar then leads a raid on Paris, facing fierce resistance and internal strife.

The season ends with Ragnar orchestrating a daring plan to conquer Paris, culminating in his shocking baptism and a feigned death to infiltrate the city. Rollo ultimately agrees to defend Paris.

Season 3 of Vikings covers episodes 1-10. Here's everything that happened:

Season 3, Episode 1: Mercenary - Ragnar and his men agree to fight for Princess Kwenthrith in Mercia in exchange for farmland in Wessex. Lagertha stays behind to lead the Viking settlers. Kwenthrith's uncle and his army are defeated, and she is restored to her throne. The episode concludes with Bjorn vowing to return to Wessex to reclaim what is theirs.

Season 3, Episode 2: The Wanderer - Following a victory in Mercia, Ragnar's forces secure Princess Kwenthrith's territory. Kwenthrith exacts brutal revenge on her uncle's head for past abuses. Meanwhile, Torstein undergoes a gruesome arm amputation due to a severe infection. In Wessex, Lagertha and Athelstan work on establishing a settlement, and a mysterious man known as "The Wanderer" begins appearing in the dreams of Aslaug, Helga, and Siggy, culminating in his arrival at Kattegat.

Season 3, Episode 3: Warrior's Fate - In Mercia, Ragnar's forces achieve victory, but at the cost of Torstein's life as he bravely acts as a decoy. Meanwhile, Bjorn faces Ragnar's wrath after his pregnant lover, Porunn, is severely injured in battle. Back in Kattegat, the mysterious wanderer Harbard continues to exert an unsettling influence, culminating in the drowning of two young boys.

Season 3, Episode 4: Scarred - Following a victory in Wessex, tensions rise among the Vikings. Siggy drowns heroically while saving Ragnar's sons from an icy pond. Meanwhile, Princess Kwenthrith poisons her brother, Burgred, solidifying her claim to Mercia. The episode concludes with Ragnar and Ecbert realizing Kwenthrith's ruthless nature.

Season 3, Episode 5: The Usurper - Upon returning to Kattegat, Ragnar learns of Siggy's death and confronts Aslaug about her negligence. Lagertha discovers Kalf has usurped her earldom, leading Ragnar to invite Kalf to raid Paris. Meanwhile, King Ecbert orchestrates the slaughter of the Viking settlement in Wessex, framing his son Aethelwulf. Rollo grapples with grief, and Ragnar seeks the Seer's counsel about the Paris raid.

Season 3, Episode 6: Born Again - Athelstan embraces Christianity, declaring he has been "born again," which deeply troubles Floki. Meanwhile, Judith gives birth to a son, revealing Athelstan as the father, leading to her punishment and the child's christening as Alfred. Floki brutally murders Athelstan, driven by religious fervor and jealousy. The episode concludes with Ragnar mourning his friend and seeking vengeance for the destroyed settlement in Wessex.

Season 3, Episode 7: Paris - The Viking fleet arrives at Paris, causing panic. Ragnar tasks a guilt-ridden Floki, who recently killed Athelstan, with leading the assault. While the Parisians prepare their defenses, Floki unveils his innovative siege towers, and the episode concludes with the Vikings poised to attack the city walls.

Season 3, Episode 8: To the Gates! - The Viking assault on Paris falters as their siege towers are burned and their attempts to breach the gates are met with a deadly trap. Bjorn Ironside is severely wounded, and Floki descends further into madness, believing the gods have abandoned him. Ragnar reveals he orchestrated Floki's leadership failure as a form of revenge. The episode concludes with the Vikings in disarray, forced to retreat.

Season 3, Episode 9: Breaking Point - A desperate second assault on Paris sees Lagertha lead a stealth attack, while Rollo proves a formidable warrior. Ragnar, gravely ill and hallucinating, negotiates peace with the Parisians. He demands baptism to reunite with Athelstan in heaven, a move that horrifies his own people. The episode concludes with Ragnar's shocking baptism, leaving his followers questioning his leadership.

Season 3, Episode 10: The Dead - Ragnar, feigning death, uses his "funeral" procession into Paris as a Trojan horse. He stabs the bishop and opens the city gates, allowing the Vikings to raid. He later releases Princess Gisla and returns to Kattegat, revealing to Floki that he knows he killed Athelstan. The episode concludes with Rollo agreeing to defend Paris.