Summary from Wikipedia:

In 2020, the unexplained strengthening of Earth's magnetic field negatively affects the planet. Layla Hassan, Shaun Hastings, and Rebecca Crane receive a signal with coordinates in New England, where they exhume a Viking raider's remains. Layla, struggling with the Staff of Hermes' influence, enters the Animus to view the raider's memories.

In 855 CE in Norway, a young Eivor Varinsdottir witnesses warlord Kjotve the Cruel sacking her hometown and killing her parents before she is rescued by Sigurd, son of King Styrbjorn of the Raven Clan. Seventeen years later, Eivor has been adopted by Styrbjorn, and pursues vengeance against Kjotve. Her latest attempt fails, but she recovers her father's axe. Touching it, Eivor experiences a vision of Odin, leading her to consult the local seeress, Valka. Valka induces another vision of Sigurd losing an arm before being consumed by a giant wolf.

Sigurd returns from an expedition with foreigners Basim and Hytham, members of the Hidden Ones, who came to Norway to assassinate Kjotve, a member of the opposing Order of the Ancients. Defying Styrbjorn's orders, the siblings enlist King Harald's help to eliminate Kjotve. Following their victory, Harald declares his intention to unite Norway under his rule. Styrbjorn pledges fealty to Harald, angering Sigurd, who expected to inherit the crown. He and Eivor take loyalists in the clan on an exodus to England, establishing the settlement of Ravensthorpe. Eivor then secures alliances with neighboring Saxon kingdoms and Viking clans led by Ivar, Halfdan, Ubba Ragnarsson, Guthrum, and Ceolwulf of Mercia, and helps Hytham assassinate local Order members, following tip-offs from a "Poor Fellow-Soldier of Christ."

Eivor's visions continue. Valka gives her an elixir that makes her dream of Asgard from Odin's perspective. Hoping to avert his own fated death during Ragnarök, Odin imprisons Loki's son Fenrir, who is foretold to kill him, and travels to Jotunheim to retrieve a magical mead that will ensure his and the other Aesir's souls will be reincarnated. Layla realizes these are actually visions of the Isu shortly before the Great Catastrophe, and that Loki, who was forbidden to reincarnate himself after betraying Odin, found another way to ensure his survival.

Sigurd and Basim discover an Isu relic, and Sigurd, with Basim's encouragement, comes to believe himself a god. Fulke, an Order agent and servant of King Aelfred of Wessex, captures Sigurd, believing him to be an Isu or descendant thereof, and tortures him, removing his right arm. Eivor and Basim kill Fulke and rescue a traumatized Sigurd. Eivor and Sigurd later travel to Norway, where they uncover an Isu temple with an advanced tree-shaped computer system. The siblings connect to it and are seemingly transported to Valhalla, where they enjoy endless battles, until Eivor realizes Valhalla is a dream-world and escapes with Sigurd after resisting Odin's influence. Outside, they are confronted by Basim, who reveals himself, Eivor, and Sigurd to be reincarnations of Loki, Odin, and Tyr, respectively. Basim, having been overtaken by Loki's personality, attacks Eivor, seeking revenge on Odin, but she and Sigurd trap him in the computer.

Sigurd abdicates leadership of the clan to Eivor. In England, Eivor and her allies join Guthrum's assault on Wessex, defeating Aelfred's forces at the Battle of Chippenham. Eivor later tracks down Aelfred, and learns that he is the Grand Master of the Order of the Ancients and the "Poor Fellow-Soldier of Christ". Disgusted by the Order's heresy against Christianity, Aelfred sought to replace it with a new God-fearing order. Eivor spares Aelfred and returns to Ravensthorpe to a hero's welcome.

In the present, the Assassins deduce the strengthening magnetic field is a result of Desmond Miles's activation of the Isu towers in 2012. To stabilize the field, Layla travels to the Norway temple and enters the simulation. She meets Basim, who reveals that he led the Assassins to Eivor, and tells her how to stabilize the magnetic field. She does so, but this releases Basim and traps Layla in the simulation. Layla encounters a being called "the Reader," and decides to work with him in the computer to prevent future disasters, allowing her mortal body to die. Meanwhile, Basim escapes the temple with the Staff of Hermes—containing the consciousness of Loki's lover, Aletheia—and meets Shaun and Rebecca. After they leave to bring William Miles, Basim enters the Animus to track down Loki's missing children.

Wrath of the Druids

In 879, Eivor receives a letter from her maternal cousin Bárid mac Ímair, now King of Dublin, requesting her assistance in Ireland. Eivor agrees to help Bárid secure an alliance with Flann Sinna, who is to be crowned High King of Ireland. After uncovering and foiling a plot to assassinate Flann ahead of his coronation, he requests Eivor's help to gather allies and strengthen his rule. Upon taking the castle of Cashelore, Eivor discovers that Flann's army has been poisoned and seeks an antidote with Flann's advisor, Ciara ingen Medba. Eivor learns that the Children of Danu, a cult of druids who seek to oust the Norse and Christian faiths from Ireland, are responsible, and begins hunting down their members. Eivor also discovers that Ciara is a former cult member, having left upon learning of their extremist ways.

In 881, Eivor uncovers the identity of the cult's leader: Eogan mac Cartaigh, the Abbot of Armagh, who feigned Christian faith. While informing Flann and Bárid, Eogan has his forces besiege Clogher. Bárid is killed in the attack, prompting Eivor to exact revenge and kill Eogan. In the aftermath, the Kings of Ireland decide to eradicate the druidic faith entirely, and Flann reluctantly agrees to launch an inquisition against the druids. Enraged upon learning of this, Ciara goes to the Lia Fáil to use its power to prevent her culture from being eradicated. She tries to take control of Flann and his men, but Eivor defeats her and the Lia Fáil is destroyed. Flann reflects on his decision and promises to be a good king for all the people of Ireland, cancelling the inquisition. Meanwhile, Eivor meets with Sichfrith, Bárid's son, who succeeded him as King of Dublin. The two reflect on Bárid's dreams, and bond as family.

The Siege of Paris

In 885, Eivor is recruited by Toka Sinricsdottir, a Viking raider from Francia, to partake in a planned raid on the city of Paris. In Melun, Eivor meets Sigfred, Toka's uncle and jarl, who seeks vengeance against the Franks for the death of his brother Sincric (Toka's father). After pushing back an attack by the Frankish bishop Engelwin—the man responsible for Sincric's death—Eivor and Sigfred follow him back to Paris, where the former assassinates Engelwin, discovering his affiliation with a secretive, zealous sect of the Church called the Bellatores Dei (God's Warriors). Afterwards, hoping to avert war, Eivor seeks an audience with the Frankish emperor Charles the Fat, who agrees in exchange for the return of his missing wife Richardis. Eivor finds her being held captive by another Bellatores Dei member, a nun known as "Little Mother", whom she kills before rescuing Richardis. The two then head to Lisieux, where Eivor meets Bernard, Charles' illegitimate but only male heir. Eivor realizes that Charles actually seeks Bernard, and that Richardis is protecting him, to prevent him from being corrupted by his father.

After meeting with and being betrayed by Charles, Eivor returns to Sigfred, just as the Viking army prepares for the siege of Paris. Still hoping for a peaceful resolution, Eivor seeks out Count Odo, Paris' military leader, but he rejects her offer of peace. As the Vikings raid the city, Eivor becomes dejected after witnessing Sigfred's bloodlust, and infiltrates Odo's palace to force him to surrender. Sigfred agrees to end the siege in exchange for a hefty sum of silver and is made protector of Normandy, abdicating leadership of the clan in favor of Toka. Later, Odo contacts Eivor, asking her to find Richardis and Bernard, who have gone missing. Eivor rescues Richardis from an ordeal by fire she was put through by an increasingly mad Charles, before confronting and potentially killing Charles. Regardless of the outcome, Odo steps in to fill the void left by Charles' absence, and Eivor returns to England knowing she has a new friend and ally in Toka.

A Fated Encounter

In 887, Eivor travels to the Isle of Skye after being informed by Valka's seeress friend Edyt that the locals having been suffering from intense nightmares. While searching for the source of the nightmares, Eivor runs into Kassandra, who has come to retrieve an artifact that has been affecting the locals' minds, turning many of them insane and violent. Realizing they share a common goal, the two agree to work together to find the artifact, although Eivor becomes distrustful of Kassandra due to the latter's secretive nature, and eventually abandons her after it is revealed that Kassandra's presence on the island is what activated the artifact. Upon finding the artifact—an Apple of Eden—Eivor is attacked by deranged warriors, but is saved by Kassandra, who then helps her de-power the Apple, saving the island. Deciding to celebrate their victory, Eivor invites Kassandra to attend a wedding, where the latter reveals that she has been traveling alone for a long time and has trouble socializing. Nevertheless, after partying together, Kassandra learns to open up to people more and she and Eivor part on good terms, with the former continuing her journey across the globe while the latter returns to England.

Dawn of Ragnarök

After Odin and Frigg's son Baldr is kidnapped by the Muspelheim warlord Surtr, the two travel to Svartalfheim amid the Muspel's invasion to rescue him. Odin fights Surtr, but is defeated, and Frigg is killed by Surtr's wife Sinmara. Left for dead, Odin is saved by the dwarves who have taken shelter from the invasion. Seeking a way to defeat Surtr, Odin rescues the dwarf leader Ivaldi from Surtr's son Glod and kills the latter in combat. Odin later fights Surtr's daughter Eysa, hoping to use her to bargain for Baldr's life. Although she escapes, Odin learns of a powerful relic called Salakar that Surtr seeks for himself. Odin retrieves the Salakar before Surtr can and obtains Eysa's allegiance.

Sinmara agrees to trade Baldr for the Salakar. However, at the exchange, Baldr is revealed to be a jötunn in disguise. Odin pursues Sinmara and finds the real Baldr, already dead. Sinmara kills Eysa for her betrayal before being slain by a grieving Odin. Odin then goes after Surtr and manages to defeat him using the Salakar, avenging his son. He returns to Ivaldi to inform him of his victory, but is greeted by Hyrrokin, who warns him that Surtr's death has started the Ragnarök. Odin vows to survive it, even if not in his current body.

The Last Chapter

Years after resisting Odin's influence, Eivor realizes she can not suppress her other half forever and, feeling she has done everything she could for the Raven Clan, decides to travel to far away lands to better understand her connection with Odin. She bids farewell to all her friends and allies, kindly rejecting offers from Hytham and Aelfred to join the Hidden Ones and the Templars, respectively, in the process, and sets off for Vinland. There, Eivor spends her final years talking with Odin, who tells her about the Great Catastrophe that wiped out most of the Isu, and how he and his kind came to reincarnate themselves throughout the ages.

In the present, these memories are being watched by Basim, who realizes Eivor's connection with Odin is different from his own connection with Loki. After completing Eivor's memories, Basim is met in the Animus by William Miles, who stipulates that if they are going to work together, he will first need a sample of Basim’s genetic material, allowing the Assassins to access Basim’s genetic memories.

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Gamerscore: 940/2110

Achievements: 46

Total Power Level: 506

Total Kills: 6,627

Distance Traveled: 1,209,776

Time Played: 8 days, 12 hours, 7 minutes (204 hours, 7 minutes)

✅ The Siege of Paris

✅ Dawn of Ragnarök

✅ Wrath of the Druids

✅ Tombs of the Fallen

❌ Forgotten Saga