Lydia is endowed with Cassandra's Tears, seizures giving her prophetic visions that are not believed. She is a slight girl, wears black dress, combat boots, her hair dyed matte black. She has a soft, sweet face, pale skin, sunken eyes, and an alley cat awareness.
Father Forthill describes Lydia as having all the signs of an abused personality. She was malnourished, had a fever, and needed a bath. He thought she might be going through some sort of withdrawal.
In the series
In Grave Peril, Lydia stops Harry Dresden as he's leaving his office pleading that he's the only one who can help her. She claims to have Cassandra's Tears. She has had three vision of a spirit coming for her. She has seen fire, wind, dark things and a dark war, and Dresden in the middle of it. Dresden is the one who can make the path go different ways. She asks him for a talisman, something for protection against the spirit, and he gives her his Dead Man's Talisman. He tells her to go to Saint Mary of the Angels Church.
The next day, Father Forthill tells Harry Dresden and Michael Carpenter that Lydia came to him, and had a seizure. Soon afterward, a frightening spirit rampaged outside the church all night demanding her. Lydia fell into despair and tried to go out to it in order to spare Forthill. He forbade her and continued to read to her from the bible. She fell asleep. She left soon after while Forthill checked the doors and windows.
Dresden tracks her with a spell using his shield bracelet and a tuning fork. He finds her unconscious in a van inside of a warehouse. The Red Court vampires, Kyle and Kelly Hamilton come out from the shadows to attack Dresden. Kelly poisons him with her spittle, the fire he started brought down the wall letting the sun in. They leave with Lydia in the van. Dresden thinks it's possible that she went to Micky Malone's and that's how the Nightmare go to him, by possessing her. Harry wonders why Bianca St. Claire wants her and what is her connection to Malone.
At Bianca St. Claire's ball, the Leanansidhe brings Amoracchius to Bianca who then gives it to Mavra. Mavra is about to unmake the Sword by sacrificing Lydia with it, transforming it an ordinary sword. Carpenter, Dresden and Thomas Raith join forces to stop her, surrounded by vampires.
Michael Carpenter bring Dresden and Lydia back to Dresden's apartment. According to Carpenter, Lydia does not want to go to sleep and he recognizes her from Leonid Kravos's lair. Dresden plans to ask her about the layout of Bianca St. Claire's place when she wakes up. When she does wake up, Lydia is possessed by the Nightmare. Dresden believes it Kravos's demon, who does everything to provoke them into killing Lydia. Carpenter can not slay it with Amoracchius because it's inside Lydia—an innocent—not a construct. Just as Dresden is about to die, he recalls the phone conversation with Susan Rodriguez and finally realizes that Lydia is possessed by Leonid Kravos' ghost not his demon and knows how to destroy it. Thomas Raith distracts Lydia by using his White Court–House Raith powers of seduction. This frees Dresden to exorcise Kravos's ghost.
After Dresden defeats the Nightmare and Bianca St. Claire, Father Forthill helps set Lydia up with the Church's equivalent of the Witness Protection Program.[Footnote 1] It turns out her real name is "Barbara".