The fourth installment in the Serafina series is set in 1900 at Biltmore Estate, the grand mansion built by George Washington Vanderbilt in the Blue Ridge Mountains of North Carolina. Serafina, a catamount shape-shifter who can transform between human and black panther forms, serves as the self-appointed Guardian of Biltmore. Her best friend, Braeden Vanderbilt, Mr. Vanderbilt's orphaned nephew and the only person who knows her true nature, has been sent to boarding school in New York to fulfill his late father's wishes. Without him, Serafina feels lost and useless, patrolling the estate obsessively, flinching at teacups and startling at shadows.
Thirteen carriages arrive for the fall hunting season. Serafina scrutinizes each guest, noting Colonel Braddick, a broad-shouldered hunter who barks orders about his rifles, and his quiet, dark-haired daughter Jess. That evening, Braeden appears on the South Terrace, pale and bloodied, having jumped off the train in Tennessee and ridden fifty miles home. He leads Serafina to a campfire by the lake and points out the Pleiades, a star cluster he calls the Seven Stars. A meteor storm blazes overhead, its light reflecting on the still water. A pure white fawn appears, and hunters wound it. Braeden rescues the fawn and spends the night healing it with his supernatural ability, while Serafina charges the hunters in panther form, scratching one across the neck.
The next morning, Mr. Vanderbilt comes to the basement workshop where Serafina lives with her pa, Biltmore's chief mechanic. Frightened by something he has seen but cannot describe, he asks Serafina to move to the second floor to watch over the house and Baby Nell, the Vanderbilts' infant daughter Cornelia. He arranges for Essie Walker, Serafina's friend and maid, to serve as her lady's maid. When Serafina checks Braeden's room, she finds no trace he was ever there. The campfire site is similarly undisturbed. She begins to doubt whether his visit was real.
At dinner, Colonel Braddick boasts about his kills and announces his intent to hunt a mountain lion at Biltmore. Serafina notices fresh scratches on his neck that match her own claws. Afterward, Jess reveals she has witnessed her father's cruelty to animals and urges Serafina to warn those she needs to warn: "Because I've seen too many dead cats" (100). Serafina races into the forest in panther form. The hounds tree her mountain lion siblings, and the colonel opens fire. A dense fog rolls in, and chaos erupts. When Serafina regains consciousness, the colonel and three other men lie dead with strange straight slash wounds. Jess is unconscious but vanishes before Serafina can help. Examining the wounds, Serafina fears she may have killed the men in a panther rage.
She finds the white fawn alive and well in a moonlit meadow, confirming the night with Braeden was real. She later deduces that he released the healed deer and returned to New York without saying goodbye. Violence escalates inside Biltmore. A guest, Mr. Kettering, is found dead at the base of the Grand Staircase, but when Serafina brings Mr. Vanderbilt to see the body, it has vanished. A gargoyle-like creature kills Serafina's cat Ember. The white deer appears inside the house, now larger with antlers, and stares at Serafina with knowing eyes before disappearing. Most disturbingly, Serafina watches what appears to be Mr. Vanderbilt attack and kill Mr. Cobere, the rotisserie cook, with an iron fire poker. Devastated, she collapses in her pa's arms. He counsels her to have faith in what she knows and keep pushing forward.
Serafina identifies her overriding duty: protect the innocent, especially Baby Nell. She finds creatures converging on the nursery through the walls and ceiling, takes Baby Nell from beside her sleeping mother, and flees in a carriage with Essie and Nolan, a stable boy. Pursuers force them off the road and the carriage crashes. Braeden emerges from an oncoming carriage, having sensed from New York that Serafina needed him and arranged a special train. Mr. Doddman, Biltmore's security manager, surrounds Serafina at gunpoint, and Mrs. Vanderbilt accuses her of kidnapping Cornelia. Braeden defends Serafina, and Mr. Vanderbilt confirms he too has seen the creatures. On the road home, they find Lieutenant Kinsley, a cavalry officer and close friend of Mr. Vanderbilt, carrying the lost Jess across a field. Jess confesses she secretly misaligned her father's rifle sights before the hunt to prevent him from hitting the mountain lions.
The white deer appears on a hilltop. When Kinsley fires, the bullets deflect, one ricocheting into his own arm. Three attackers charge from the trees: a woman in medieval plate armor and two massive African lions. Serafina shifts into panther form and kills all three. When she touches the dead warrior's face, it feels like limestone; the lions' bodies feel like Italian rose marble. She realizes these are Biltmore's own statues come to life: the front-door lions, Joan of Arc from the facade, and Saint Louis with his longsword. The bronze statue of Mr. Vanderbilt was the doppelgänger that killed Mr. Cobere. Serafina is flooded with relief that Mr. Vanderbilt is innocent.
In the Library, she and Braeden discover that according to ancient druidic beliefs, when the Pleiades rise high each autumn, the veil between the physical and magical worlds thins. If the Seven Stars are caught in a reflection, their magic manifests whatever is occurring at that moment. The night by the lake, the stars reflected on the still water at the instant the hunters shot the fawn. The violence became the template for all that followed, and Braeden's healing sustained the enchantment by keeping the deer alive. The initial victims were all connected to hunting, and each act of defense strengthens the magic further.
As Serafina urges evacuation, the house erupts. Every statue and carved creature comes to life. Jess shoots the bronze doppelgänger when it attacks Braeden. Serafina charges through the house in panther form with Braeden on her back. On the Grand Staircase, she tackles her pa from the path of the falling chandelier. Lying face-to-face with her panther form, her pa recognizes her with amazement, pride, and love. She draws the army away from the fleeing household, sprinting up Diana Hill while Jess snipes gargoyles from the tower.
In the forest, a wyvern, a dragon-like creature animated from a rooftop statue, seizes Braeden and carries him above the treetops. Serafina presses on to the Angel's Glade, an ancient cemetery clearing centered on a winged stone angel, the one place the creatures cannot enter. Surrounded, she throws a rock at the white deer to provoke it into animating the angel as a weapon against her. Unlike every other statue, the angel possesses her own spirit and cannot be controlled. She walks toward the white deer and swings her sword in a great arc that tears open a rift between worlds. The deer and all enchanted creatures explode into blazing fragments that streak upward like a reversed meteor storm, returning to the Seven Stars.
The angel kisses Serafina's forehead, then returns to stone. Serafina finds Braeden pinned under the wyvern's stone remains in the flooding swamp and frees him. They return to the damaged estate, find a lone black thoroughbred in the rear paddock, and ride out to rejoin the search party: Mr. Vanderbilt, Jess, and Serafina's pa, all looking for her.
In the aftermath, funerals are held and Kinsley recovers in the hospital. Mr. Vanderbilt commissions new statues but omits the most dangerous ones. Braeden proposes using his inheritance to found a school at Biltmore for himself, Serafina, Jess, Baby Nell, and the children of servants, and asks that hunting be permanently banned on the estate. Mr. Vanderbilt agrees. That night under the stars, Braeden tells Serafina he could always see Jupiter from New York and imagined it was her, just as she had imagined it was him. Serafina rests her head against his chest and whispers that she loves him. He whispers the same in return.