In a prologue, a woman named Lizette bathes in a river after a sexual assault, using an innate ability to heat water. A blue butterfly lands on her stomach and melts into her skin. The narration frames this as giving life rather than taking it, foreshadowing the cycle of rebirth central to the story.
The main narrative begins in August 1955. Darcy O'Sullivan, a 24-year-old orphaned English teacher at Saint Russell Boarding School in Boston, receives a letter from lawyer Mordechai Vaughan: Her biological father, Leo Pierce, has died and included her in his will. The envelope contains $1,000, a swan brooch, a key, and a train ticket to Fairydale, Massachusetts. Darcy visits Sister Mary and Sister Anne, the nuns who raised her at a Worcester orphanage, who confirm Leo funded her upbringing through anonymous donations. Feeling betrayed, Darcy departs for Fairydale with Jane Austen's
Northanger Abbey, whose heroine imagines gothic horrors that prove unfounded. This parallel becomes a recurring motif as Darcy encounters genuinely supernatural events.
Darcy's journey is marked by eerie occurrences. At Ipswich, a thief steals her suitcase, and she learns no railway reaches Fairydale. Vaughan drives her the rest of the way. When they cross the town border, a violent storm erupts, yet Darcy does not get wet standing in the rain. Papers she collects spell out "Don't. Trust. Them." Leo's wife, Vicky Pierce, and Darcy's half-siblings, August and Grace Pierce, receive her with hostility. Vaughan installs Darcy in a remote house at 12 Astor Place, across from the sealed Old Church. That night, she hears organ music from the supposedly empty church and, upon investigating, meets Caleb Hale, a striking man from the Hale family's manor on the hill.
The narrative interweaves Darcy's waking life with vivid dreams of a past existence. In these visions, she is Lady Elizabeth Montford, a 17-year-old in 1789 England who looks identical to Darcy. Elizabeth encounters Amon d'Artan, a mysterious nobleman who rescues her from an attempted rape by killing her attacker with a hand that transforms into a blade.
At Leo's funeral, Darcy accidentally breaks open his casket, revealing he is alive. Leo curses at her, vomits his organs, and disintegrates in black flames. The townspeople brand Darcy a witch. The Hale family, led by matriarch Rhiannon Hale, offers help. The reading of Leo's will grants Darcy $1 million and 12 Astor Place, contingent on her residing in Fairydale for two months. Darcy's relationship with Caleb develops rapidly; he is charming yet possessive. After a cabin incident involving terrifying hallucinations, a doctor confirms Darcy sustained a head injury that could cause such episodes. Three people who wronged Darcy are found brutally murdered and displayed on the town monument. A fire destroys her house, but she escapes unscathed and wakes in the Hale manor.
Darcy's dreams continue. As Elizabeth, she reunites with Amon at a masquerade, only for Elizabeth's mother, Fiona, to shoot him. Darcy wakes devastated to find her injuries healed overnight. At the manor, a faceless creature called a Kiaka attacks Darcy before an invisible force destroys it. Connor Hale, a member of the family, confirms the house harbors real ghosts, and Darcy receives whispered messages from what she believes is Amon's spirit.
Rhiannon reveals that her grandmother, Lydia Hale, prophesied that someone born with a healing birthmark would eradicate or unleash Fairydale's evil. Rhiannon claims Amon is an archdemon sealed in the Old Church since 1805 who killed Elizabeth and triggered a plague, and she asks Darcy to help destroy him. Separately, Archibald Nicholson, the powerful town patriarch, tells Darcy he is her maternal grandfather and proposes an alternative blood ritual. When Darcy touches the gemstone on Nicholson's cane, she sees herself as Sela, married to Amon in ancient Rome without the birthmark, suggesting he loved her independently of any power. Darcy realizes both factions are manipulating her.
At the Fairy Festival on the beach, gargoyles attack. Darcy heals a child's broken leg by channeling energy through her hands, discovering that doing so severely depletes her strength. Caleb proposes marriage, and Darcy accepts, though she remains conflicted about Amon. Rhiannon reveals she is Darcy's true maternal grandmother: Nicholson assaulted Rhiannon, fathering Darcy's mother, Lizette, and Leo Pierce similarly assaulted Lizette to father Darcy. Rhiannon then shows Darcy a fabricated collective memory depicting Amon killing Elizabeth. Shattered, Darcy resolves to commit to Caleb.
Extended visions reveal the full truth. In Elizabeth's past, Fiona disclosed their family's membership in the Coven of Light, a lineage of witches who fight demons, and warned that Amon was a dangerous archdemon. Despite these warnings, Amon married Elizabeth under an alias, and they relocated to the American colonies, building the manor that became the Hale house. They adopted Elizabeth's deceased sister Olivia's three children: Abraham, Abel, and baby Lydia. The truth of Elizabeth's murder emerges: Abel, not Amon, killed Elizabeth and Abraham in the Old Church. Abel had secretly allied with Kress and Finn, Amon's former comrades from his homeworld, Arkgor, and stole Elizabeth's magical necklace. Amon arrived too late; his grief triggered a catastrophic energy release that killed everyone nearby, the event recorded as a plague. The coven's elders sealed Amon in the church at the cost of their lives. Abel then assumed the identity of Archibald Nicholson and exploited the necklace's power for nearly two centuries.
Darcy and Amon confront Abel, recover the gemstone, and Darcy executes him with a fire spell. They find Lydia Hale alive but trapped in perpetual near-death by Abel's sorcery. Lydia, who spent decades secretly arranging events to reach this outcome, asks her parents to grant her death. Amon fulfills her request.
When Amon places the recovered gemstone around Darcy's neck, it fuses with her body, restoring all her memories as Sela, her original identity. Sela was born on Arkgor with unprecedented healing abilities. Her mother, Elora (later known as Fiona), kept her isolated. Amon, the Shadow General of the Vissirian Empire and a part-Reva warrior—the Reva being a nearly extinct species with extraordinary matter-manipulation abilities—recognized Sela as his destined mate. They married and fled Arkgor to Earth after he was falsely accused of assassinating the emperor. During their escape, Elora cursed Sela's womb. They lived on Earth for thousands of years until a sorcerer named Ambrosius stole Sela's power through deception, leaving her to die. Amon performed a forbidden spell that preserved her essence, allowing her to be reborn, first as Elizabeth, then as Darcy. Amon also reveals he has been projecting himself as Caleb throughout Darcy's time in Fairydale using astral projection, while remaining physically imprisoned in the Old Church.
With her identity restored, Sela and Amon infiltrate the coven's gathering. Amon disguises himself as an Elder and has Mrs. Ito, a coven member who can read an object's history through touch, confirm that he did not kill Elizabeth. In the chaos, Darcy and Amon access the six codices, collections of forbidden spells divided among the witch families, and perform a spell that shatters his prison. Darcy then neutralizes Kress and Finn's protective shields, and Amon kills them both.
Five months later in Rome, Darcy discovers she is pregnant with twins. Her restored powers, strengthened through each rebirth cycle, have healed the curse on her womb. Sela convinces Amon to return to Arkgor and lead a rebellion against the empire. In a bonus epilogue, Amon enters the emperor's tournament arena in disguise, defeats all opponents, reveals his identity, kills the emperor, and kneels before Sela, declaring her empress as their newborn twins rest against her chest.