Wisteria, the third and final installment in the Belladonna trilogy, opens with a prologue set centuries before the main story. Life, a deity named Mila, rests beneath a wisteria tree beside her husband, Fate, watching him weave a human destiny into a tapestry. Mila's body has aged, and she has secretly arranged for Fate's brother, Death, to take her so that her soul can reincarnate and new souls may continue to be born. Death believes he can preserve her memories, but only if her passing is peaceful. When Mila tries to explain, Fate refuses to let her go. He binds her with golden threads, silencing her, and strikes a desperate bargain with Death. The bargain backfires: Mila's death becomes agonizing, ensuring she loses all her memories upon reincarnation.
Centuries later, Blythe Hawthorne marries Aris Dryden, who poses as a foreign prince but is actually Fate in human guise. Their union is not born of love. In the previous book, Blythe spilled her blood onto one of Aris's golden tapestries to free her father, Elijah, from a false murder charge, binding herself to Aris in the process. A glowing band of light on each of their ring fingers now marks the bond. At the ceremony, Elijah slips a knife into Blythe's luggage and establishes a coded system for their future letters so he can verify they are truly written by her hand.
After the wedding, Aris sends Blythe away in a carriage, but the bond transports her back to Wisteria Gardens, the palace that serves as his home. The palace has been stripped of all grandeur: bare gray stone, no staff, no heat, and a stone slab for Blythe's bed. During Aris's daily absences, Blythe discovers a hidden hallway leading to Life's old suite, where she finds portraits of Aris dancing with a silver-haired woman and a hand mirror of polished obsidian, which she takes. Intrusive visions of dancing with a faceless man to a familiar melody have plagued her for months, strengthening her suspicion that Life's presence lingers in the palace.
A tentative truce forms when Blythe finds Aris weaving tapestries one night. Each color represents an emotion; together they compose the story of a human life. She challenges his detachment, and he begins making small concessions. When Death transports Blythe to visit her cousin Signa Farrow at Foxglove, Signa's estate, Signa tries to reveal something important about Aris, but the band of light burns each time she speaks, blocking the revelation. Death also reveals that the rings bind Aris to Blythe as much as they bind her to him. Blythe finds Aris on a nearby shore, confirming he has been secretly tethered to her all along. In the argument that follows, Blythe tells Aris that Signa will never return his feelings and declares she will not look away from him no matter how brightly he burns. The words shake him visibly, because Life said the same thing during their first argument centuries ago.
When Elijah announces a visit to Verena, the fictional kingdom Blythe invented in her letters, she and Aris strike a bargain: If he can fool Elijah, Blythe will travel with him. Aris transforms Wisteria into an ice palace and transports it to a northern town called Brude, conjuring enchanted staff and puppet royals. During the visit, Aris is unexpectedly kind, defending Blythe's autonomy when Elijah tries to shield her from troubling news. On a sled ride, Blythe cuts her palm, but the wound heals instantly, and she notices fresh grass growing in December snow. Forced to share a bedroom to maintain their newlywed charade, the two grow closer. Aris confides he has not been intimate with anyone since Life's death, and during a game of charades he hums a waltz that Blythe recognizes as the melody from her visions.
After Elijah departs, Aris reveals that Wisteria's front door can open anywhere in the world. In a summer glade, they share a passionate kiss, but Aris pulls away, disturbed by the intensity of his feelings. When he later discovers Life's obsidian mirror in Blythe's armoire, he vanishes in anguish. Days later, Blythe commands Wisteria's door to take her wherever it wants. It opens onto her mother Lillian's vandalized garden behind Thorn Grove, the Hawthorne family estate. Overcome with grief, Blythe's tears cause wolfsbane and ivy to erupt from the soil. She envisions a wisteria tree and watches it grow from nothing; frog skeletons reassemble and spring to life. The truth crystallizes: the healing of a dead horse months earlier, flora erupting in her father's study, and wounds that close instantly all belong to Blythe. She is the reincarnation of Life. It was never Signa that Aris was searching for.
At Thorn Grove, Blythe encounters Solanine, a mysterious deity with flame-red hair whom Blythe later identifies as Chaos incarnate. Solanine's touch floods Blythe with visions of destruction, and when she tries to kill Blythe, thorns erupt from Blythe's skin in self-defense. Solanine declares that Blythe has upset nature's balance and gives her one chance to fix her mistake. At the Thorn Grove Christmas ball, Blythe's powers spiral out of control until Signa coaches her to retract the thorns and ivy erupting from her skin. Signa confirms she has known about Blythe's true identity but was physically unable to speak of it due to the bond's magic. Aris arrives, publicly defends Blythe, and the two share a kiss on the dance floor before Blythe faints. He carries her back to Wisteria, now decorated for Christmas, and gifts her a blank room that responds to her imagination. Together they build a fantastical library, and their growing closeness leads to intimacy.
Blythe's illness worsens rapidly. She coughs blood and recognizes symptoms identical to belladonna poisoning, though no poison is in her system. In a vision, Mila appears and explains the single inviolable rule of Life's power: she must never bring anyone back from the dead, because doing so summons Chaos. Mila urges Blythe to "fix what has been set in motion" (287). Blythe, Signa, and Death attempt to kill the horse Blythe accidentally resurrected, hoping to restore balance, but Life's blessing has made it immune to death. Following visions of her mother Lillian's ghost, Blythe discovers her brother Percy Hawthorne hiding in Lillian's old room at Thorn Grove. Percy, who was supposed to be dead, has been unknowingly resurrected by Blythe's awakening powers. His blood runs black and his eyes are colorless. In the previous book, Signa gave Percy's remaining years to Blythe to save her life; his resurrection is now draining those borrowed years, killing Blythe.
Aris, Death, and Signa converge on Thorn Grove, but none can kill Percy; Life's blessing protects him. Solanine materializes, explaining that since Percy's resurrection stole the years sustaining Blythe, her life is the price, and a single human soul cannot balance the scales for a deity. Blythe accepts her death, asking that Elijah never learn the truth and making Signa promise not to reveal her true identity to Aris. But Aris has already discovered that Blythe's tapestry has turned solid silver, Life's unmistakable color, and knows who she is. He traps Blythe in a magical pocket world of wisteria petals and a river of stars, then drops to his knees before Death and offers his immortal life for hers: "Give her my years, brother. Give her all that I am, and save her" (399). Death accepts. Before dying, Aris curses Percy to wander reviled and miserable for the rest of his unnaturally long life. As Aris's threads wink out of existence, Blythe is restored to full health.
Weeks of grief follow. Thorns erupt from Blythe's body, sealing Wisteria from the world, and the palace reverts to bare stone without Aris's magic. Elijah comes to the doorstep every day, telling stories of Lillian through the barred door until Blythe opens it. Over months, they repaint Wisteria's walls by hand, filling the home with memories in place of magic. Blythe reconciles with Signa and Death, and the three work together to master her abilities, knowing Solanine will one day return.
The epilogue jumps 27 years. Blythe has stopped aging; her hair has turned white and her eyes gray, matching Life's appearance. One day, golden threads appear on Wisteria's front door. Blythe grasps the handle and commands, "Take me to my husband" (419). The door opens onto Brude, where a man with an unfamiliar face but unmistakable golden eyes stands among falling wisteria petals. Aris whispers, "Hello, Sweetbrier [...] I've finally found you" (419).