Abbess Ingeborg (died 874), also known as The Firebrand, was an advisor to Audun during the 870s. She was also a member of the Red Hand, and a member of the Order of the Ancients' Wardens of Law sect who held the title of Preost. She resided in the Roman district within the city of Jorvik.
As a child, an angry priest once scrubbed Ingeborg's tongue with soap for spewing "heresies and lies" that ran counter to Christian doctrine. On that day, Ingeborg learned that knowledge was power, controlled by the Church. She then rose through the Church hierarchy, but the Order offered her even more knowledge and thus more power.
Eivor Varinsdottir first learned of her cryptonym of The Firebrand when Hytham told Eivor the news of three more Order targets in Jorvik. After discussing with Randvi and pledging herself to Jorvik, Eivor travelled to the city to meet up with her old friends, Ljufvina Bjarmarsdottir and Hjorr Halfsson. After finding Ljufvina, who survived an assassination attempt from the Red Hand, Eivor travelled with Ljufvina to Hjorr and then discussed with both of them of her targets in Jorvik. Upon of learning of thefts of Christian texts, Eivor set out to find out who was behind these crimes.
Eivor then travelled to Jorvik's Archives for any clues about the recent Christian texts thefts. While investigating, Eivor caught Auden and Abbess Ingeborg off-guard. Eivor then asked Auden of the recent thefts and Auden confirmed them as well as the destruction of these texts. He then told Eivor of how the Abbess was taking precautions and was in charge of safekeeping of the archives itself. During their conversation, Abbess Ingeborg stated her suspicions of the rectory and its bishop. She laid claims of meetings in the dark between the bishop and the priests. From her findings, Eivor headed to the Rectory.
After Eivor found scared priests self-contained in their houses, one priest was told to lead her to the missing bishop's house. Upon entering his locked-down house, Eivor investigated and found both burnt Christian texts and the bishop, burnt to his death on his chair. Eivor learned of his forced cooperation of the burnt texts and the suspicious manner of the Abbess' control over the texts from the Bishop's charred confession letter. Eivor set her sights on The Minster, but was immediately ambushed by the Red Hand.
Upon arriving at The Minster, Eivor witnessed the burning of more texts and a confrontation between a priest and the Abbess, who was accompanied by her henchwomen. Throughout the confrontation, Ingeborg declared all the texts and writings burning to be 'lies,' which lead to a priest retorting that she had gone mad. Having had enough, Ingeborg grabbed the priest by the throat and tossed him into the fire alongside the texts, killing him. Ordering for the whole lot of texts to be burned, Ingeborg ordered her henchwomen to continue, and one of the henchwomen revealingly replied, "Yes, Firebrand." Learning that the Abbess and The Firebrand were one and the same, Eivor followed Ingeborg, assassinated her, and ended her fiery rampage.
- Like The Seax, Ingeborg had henchwomen who looked like her and thus making her the one of two English Order members to have decoys.
- Like certain members of the Order in England, Ingeborg's Memory Corridor cutscene differs, as her soul disappeared through self-immolation by a red-turned-blue fire. Usually, Eivor takes the Order's medallion off the apparition's body.
- Ingeborg shares many similarities with the character Jubair al Hakim from the 2007 video game Assassin's Creed. Both are scholarly heads of their religion—Christianity and Islam, respectively—and are so fanatically devoted to ensuring their religion's purity that they burn texts considered heretical, proclaiming that the works "are covered in lies. So long as they exist, [the public] cannot hope to see the world the way it truly is", before shoving a priest who denounced their actions into the pyre. They also have disciples wearing the same outfits to lure the protagonist during their assassination.