" Zilpha is Horace Delaney's child by his second marriage and James Delaney's younger half-sister. Married to Thorne Geary. A devout Christian." 
Zilpha Geary was a young woman with olive skin, long black hair often tied up in a bun, and delightful brown eyes. Zilpha wore fine clothes, emphasising her beauty and social status. Her seemingly fragile appearance hid demons of her own, prancing behind the apparent look of a devoted wife.
Zilpha Delaney was the estranged daughter of Horace Delaney and his second wife, as well as the younger half-sister of James Delaney. At some point in their youth, Zilpha and James fell in love and engaged in an incestuous relationship that ended badly, with James leaving without looking back. At some point, Zilpha married Thorne Geary and cut off any contact with her father.
Seeing a Ghost
Zilpha Geary took part in the funeral cortege of her father riding a horse, proceeding slowly behind the carriage with the casket. In the church, she was deeply affected by the appearance of her brother, long believed dead. However, when the two siblings tried to interact, her husband stepped between every attempt at dialogue. Thorne was an obstacle even when Zilpha tried writing to her brother, forcing her to rewrite the letter. The couple had several unpleasant conversations about the inheritance and ways to get rid of James, and Zilpha was quite amused by the empty threats of her husband. 
Zilpha received a blank letter from her brother, accompanied by a rough diamond that she immediately put away safely in a locked jewellery box. During the reading of the last will and testament of the late Horace Delaney, it came to light the absence of Zilpha from her father's will who, instead, left everything to James. This caused resentment in her husband, but Zilpha managed to convince him to leave the office without tantrums. Later that night, Zilpha was approached by James during an orchestra concert, having a brief, however unpleasant, conversation about their feelings. Not entirely repressed or forgotten. 
Vaguely seduced by the passionate letters from James, Zilpha struggled to hold back her heart beating in her chest, repressing her feelings toward her step-brother by reminding James – and herself – that she was a happily married woman now, moreover, with a fervent Christian. However, Zilpha agreed to secretly meet James in a church, where the two shared a supposed farewell kiss. Once home, Zilpha was scolded harshly by her husband in front of the servants during dinner. The discussion concerned her monthly period, apparently evidence of her failure to conceive a child for Thorne. Choking back tears of humiliation, Zilpha was shocked by her husband's allegations about her "perverse desires". 
Zilpha received a nocturnal visit from James in a dream, during which they had sexual intercourse consummated somewhere between dream and reality, desire and nightmare. Zilpha even began to murmur words in the Ashanti Twi language, waking with a start only when she then recited a Christian prayer to ward off the evil visions. Frightened and wrapped in blankets, she was raped by her drunken husband just returned home after a bender. Invited to the soirée of Countess Musgrove, Zilpha needed to have a word with James at first, and then with Lorna Bow. When the party degenerated into an orgy and then into a fight between James and Thorne, Zilpha was shocked when her husband challenged her brother to a duel. 
Anxious about the outcome of the duel, Zilpha embraced her husband when he returned home and asked what happened, but the two soon began to argue because Thorne doubted the love of his wife, and claimed she desired to see him dead. Overnight, Zilpha murmured James' name while sleeping, unfortunately in the presence of her husband. He then dragged her out of bed and beat her violently about the face. Frightened and in pain, Zilpha was further humiliated by her husband, who had hired a priest to exorcise her. Tied to the ground in a circle of candles, she was forced to endure the ritual, including the priest handling her breasts while intoning verses of Psalms in Latin. After the ritual, Zilpha returned to the bedroom, pulling a long hat pin from the dresser drawer, looking with loathing at her husband asleep on the bed. 
The Price of Freedom
When Lorna Bow showed up at Geary house looking for information on James, Zilpha supported her husband against the alleged step-mother, with her face swollen from beatings and voice weak. After driving the woman out, Zilpha sought refreshment in a hot bath but was disturbed by her husband with whom she conversed coldly. During the night, she gathered enough courage to kill her husband with the hatpin inserted through the chest cavity. Thrilled by the act, she went straight to Delaney Mansion during a storm, embracing her brother, finally free from her abusive husband. Zilpha claimed to have done "What he (James) told her to do." However, she did not receive the welcome she expected, as James promptly sent her home, saying that he would get rid of her husband's body so she wouldn't hang. Preparing for the funeral, Zilpha pinned her hat with the same pin with which she had killed her husband. After the funeral ceremony, Zilpha made love to James and was almost strangled during intercourse, since James was prey to strange, disturbing visions.
Following her husband's funeral, Zilpha began to fantasise about resuming the relationship with her half-brother but was dissuaded from carrying out her intention by James himself, who offered Zilpha one of his rough diamonds so that she could continue to live in comfort. She burst into tears, realising that she had killed her husband for nothing. 
In despair, Zilpha decided to end her life by jumping into the Thames. She announced her decision in a letter to James, in which Zilpha claimed to yearn for peace that she had been denied in society, asking him to keep a memory of her. Whilst her soul was destined to Heaven, or perhaps to Hell because of their love or the murder she committed. After Lorna discovered the suicide by reading the letter, James told her that if Zilpha had really drowned, he would have felt it. Despite James's refusal to accept her death, after killing Dumbarton, James had a vision involving Zilpha. In the vision they were both underwater and, after kissing, Zilpha promised they would see each other again, but assumed the semblance of a drowned corpse carried away by the waves. Her fate is, therefore, unknown.
- "Whatever happens with this business of inheritance, and no matter if it results in dispute, I hope I can trust you to keep the secrets of the past buried. Buried in a deeper grave."
- ― Zilpha in a letter addressed to James
- Thorne Geary: We will haunt this n— to justice!
- Zilpha Geary: He's already haunted. Come.
- ― after discovering the last will and testament.
- "This is very simple, James. Take away a little ancient history. You live in the East, I live in the West, there are no practical difficulties."
- ― Zilpha to James
- "Dear James, at last, I have found a way out of the cage in which I have been living. Eyes I didn't know I had were opened. I saw the limits of my life, the iron bars around my soul. At last, I found a way to slip between them. I intend to leave society, leave London, leave England behind, travel to a place where I will be free. It is a place where, someday, I hope we will meet and be happy. [...] I'm planning to journey to heaven, James. I've realised the truth. My cage is my flesh, I can shed it. The River Thames will take me to God. Death is just the turning of a key in a lock. Whether God will accept me is another matter, perhaps my husband will have spoken of my betrayal. Or perhaps my feelings for you, unforgivable feelings for you, will mean the Thames will take me to a different place. Whatever my destination, if you survive your recklessness, please, keep some part of my soul inside your own."
- ― Zilpha's last words
- Season 1
- Her full name is Zilpha Annabelle Geary, née Delaney.
- In the fifth episode, the exorcist said that Zilpha was possessed by a "Barbason". The name of a demon or fiend mentioned by Shakespeare alongside Lucifer and Amaimon in "The Merry Wives of Windsor."
- In "Episode 3", Zilpha's address can be seen on one of James's letters. The address reads "Buckland Place, Chelsea." Buckland Place does not appear on any maps of Chelsea dating from 1810-1817, but it may be a reference to Buckland Manor, an English country home.
- Addressing incest between James and Zilpha, actress Oona Chaplin expressed her support for portraying such shocking themes, forcing the audience to face issues head-on. 
- Despite Robert is believed to be Horace Delaney's illegitimate son, there is the possibility he was conceived by Zilpha and James before he left England towards Africa.