Thyri is introduced in "Trial" where her father, Earl Haraldson, offers her in marriage to Rollo in exchange for testifying against his brother Ragnar. Although Rollo seriously considers the offer, he eventually chooses not to betray his brother, or more accurately, not to betray Lagertha.
In "Raid", Thyri is seen sitting beside her father during a feast, when her father's guest, Earl Bjarni, arrives. They soon find out that Earl Haraldson has arranged for Thyri's marriage to the much older earl for twenty pounds of silver, an arrangement about which both Thyri and her mother Siggy are evidently displeased.
Thyri's husband-to-be begins telling her about their future together, particularly their wedding and the sons he expects from her, all the while promising her gifts when he returns later that year. He then gives Thyri a ring, but she is still obviously repulsed.
As winter and the wedding approached, Thyri began to wistfully glance at Rollo, whom she had been interested in when the prospect first came up. On the wedding day, Earl Bjarni was enthusiastic about bedding his young bride. Thyri, on the other hand, was repulsed at the thought but was left with no choice. The newlyweds proceed to the matrimonial chamber. However, Thryi was later left lying in bed, fully clothed, with the earl deep in sleep and snoring beside her. The fat, old earl, more the worse for wear from too much ale, passed out before they could consummate the marriage.
In "Burial of the Dead", we see her husband's true nature as he complains about Thyri's lack of enthusiasm in bed, and demands that she get up after they have sex and fetch him some pickled herring - or be beaten for disobeying. Later, immediately following her father's defeat and death at the hands of Ragnar in single combat, Thyri is saved from her miserable marriage by Siggy, who stabs Earl Bjarni to death in front of the entire village. As the old earl dies, Thyri looks at her mother with gratitude written all over her face.
In "Sacrifice", after the loss of his son, Ragnar informs the group that they will head to Uppsala to pay tribute to the gods - meaning both human and animal sacrifice. As the night wears on, the Christian captive Athelstan takes a hallucinagenic mushroom, causing him to wander around in a drugged state while the others partake in other drugs and love-making. He finds Thyri, who kisses him and brings him into her tent to bathe him. Athelstan asks why she does this, although she only responds that she "must." It is unclear whether this bath leads to anything more intimate, but by morning it becomes clear that Athelstan was brought as a sacrifice.
However, Athelstan is deemed unfit to be a sacrifice as he still wears his cross, hidden beneath his sleeve. Leif, one of Ragnar's followers, gladly offers himself up as this is seen as a great honor. Thyri and the others somberly watch as first the animals and then the humans are killed to appease the gods.
Thyri is among those who perished in the plague that hit the village.
Thyri later appears in a vision to her mother Siggy before she drowns in the lake after having saved Ragnar's sons.
|Season one appearances|
|Rites of Passage||Wrath of the Northmen||Dispossessed|
|Trial||Raid||Burial of the Dead|
|A King's Ransom||Sacrifice||All Change|
|Season three appearances|
|Mercenary||The Wanderer||Warrior's Fate||Scarred||The Usurper|
|Born Again||Paris||To the Gates!||Breaking Point||The Dead|