As preordained, Illyria's sarcophagus is teleported to Los Angeles, but is held up at Customs. Doctor Sparrow maneuvers Gunn into releasing the sarcophagus in exchange for fixing his brain enhancements. Knox, Illyria's self-fashioned Qwa'ha Xahn (High Priest) and the mastermind behind her resurrection, has the sarcophagus delivered to Winifred "Fred" Burkle at the Wolfram and Hart science lab. Curiosity draws Fred to the sarcophagus and she touches one of the coffin's embedded crystals, releasing Illyria's essence into her own body. Illyria's essence acts as an infection that liquifies Fred's organs, hardens her skin and allegedly consumes her soul. After hours of agony, Fred's body is completely taken over by Illyria, who also absorbs her memories (likening them to "sparks"). Illyria, with the aid of Knox, attempts to bring about the destruction of humans by resurrecting her vicious ancient army, but soon discovers that it was destroyed long ago.

Lost and without purpose, Illyria agrees to learn how to adjust to the modern world with the help of Wesley, who is drawn to the being that now occupies the body of his love. Illyria spends her nights with the oft-drunk Wesley and her days wandering the corridors of Wolfram and Hart. When Wesley mentions to her that Gunn is trapped in a Wolfram and Hart-imposed psuedo-hell, she opens a portal and rescues him without hesitation, later noting the great debt that the group owes to her. At this point, her pastimes include talking to plants and training with Spike, or, more accurately, beating him up while he records the details on a clipboard (Illyria: "I have been hitting the half-breed. He makes noise."). Although she criticizes Spike's adaptibility (declaring adaptation to be a compromise), she enjoys hurting him; at one point, she expresses her desire to keep him as a pet.

Eventually, Illyria's power becomes extremely unstable. To others, the Old One appears to be going mad. In truth, Illyria is being thrown out of linear progression of the time line, altering her perspective as her power seeks a way to escape its shell. Before Illyria detonates, which could potentially cause devestating destruction, Wesley uses a "Mutari generator" to extract much of her power, effectively ending the threat. Illyria is stripped of much of her superstrength, as well as her abilities to alter time and talk to plants. She grows bitter and withdrawn after the loss of her powers, which she considers a significant defeat. Her primary emotional connection is with Wesley, who continues to help her adjust to the world. After recognizing Wesley's feelings for the "shell" of Fred, she wishes to explore her relationship with Wesley in a more sexual or romantic direction; however, he rejects any possibility of accepting her in Fred's form. She also develops a connection with Spike, who can relate to her new-found situation and treats her with acceptance and dignity, communicating easily with her and helping her venture into the world.



Illyria is brutally beaten and humiliated by Marcus Hamilton, which fuels the Old One's extreme anger and motivates her to join the final battle against the Senior Partners. In the series finale, "Not Fade Away", Illyria, Wesley, Gunn, Lorne, Lindsay, and Angel each fight separate groups of demons from the Circle of the Black Thorn. After killing her demon victims, she seeks out Wesley and finds him dying. Perceiving his imminent death, Illyria comforts him in Fred's form. Grieving for him uncontrollably, she violently dispatches his murderer, an action that does not begin to assuage her grief and leaves her with a strong desire to "do more violence". Her wish is granted when the Senior Partners send their army against the gang; she joins Angel, Gunn, and Spike in the final battle against the Senior Partners.

According to rumours about a possible spin-off, mentioned by Joss Whedon and Amy Acker, Illyria survived the final battle against the Senior Partners of Wolfram & Hart. However, despite this, her current status is unknown.

The full scope of Illyria's power is unknown. When Illyria takes over her new "shell", she has tremendous physical strength. Spike likens a blow from her to being hit by a Mack truck. Her strength, reflexes, and agility make her a formidable hand-to-hand combatant. She uses an ancient fighting style that Spike compares to Tae Kwon Do and "Brazilian Ninjitsu" (probably Capoeira). Although Spike's adaptability gives him an occasional advantage, Illyria generally dominates their sparring sessions. Her skin is a hardened shell, providing her body with a heavy armor capable of withstanding blows from forged weapons (e.g. swords or axes).

She is aided in combat by her ability to selectively alter time, which allows her to easily dodge both attacks and bullets; she can accomplish a goal and leave an area before her opponent even realizes she has moved. She can also open interdimensional portals. In the episode titled "Underneath", Wesley comments on her not needing to sleep.



She can alter her physical appereance on a basic level, and she is capable of recreating Fred's persona accurately enough to fool Fred's parents. She tells Knox that she can take any form she chooses. Her senses are enhanced, which enables her to recognize that Connor's body warms when he sees her, indicating his lust. She communicates with flora, often spending hours at a time communing with a plant. Illyria is also capable of distinguishing humans (or "primitives"), from demons, vampires and other half-breeds. For example, she perceives that Marcus Hamilton is neither human nor demon (referring to him as a "creature"). She also retains the insights from her experiences as an Old One, which enable her to effectively analyze the power dynamics, personal motivations, and emotions that influence those around her.