The third installment in the
Blue Bloods series opens with a prologue foreshadowing the climax: Schuyler Van Alen watches her grandfather Lawrence battle a blinding white adversary atop Corcovado Mountain in Rio de Janeiro. Oliver, her best friend, urges her to strike, and she raises her mother's sword but misses.
The story returns to New York, where Schuyler, a half-human, half-Blue Blood vampire, adjusts to life in the household of Charles Force. Charles, the archangel Michael in this cycle of reincarnation, is the former Regis (leader) of the Blue Bloods, a secret society of vampires descended from fallen angels. He won legal custody of Schuyler after contesting her late grandmother Cordelia Van Alen's will and now forbids Schuyler from seeing Lawrence, the current Regis, and from associating with Oliver Hazard-Perry, her human Conduit (trusted human servant) whom she has made her familiar by taking his blood. Their bond is maintained through the Caerimonia Osculor, the Sacred Kiss. At Duchesne School, Schuyler endures petty torments from Mimi Force, Charles's daughter, but finds an ally in Bliss Llewellyn, a fellow Blue Blood who befriended Schuyler after Schuyler testified truthfully at Mimi's blood trial, a judicial hearing before Blue Blood authorities, in Venice.
Mimi, whose true identity is Azrael, the Angel of Death, takes Charles's seat on the Conclave of Elders, the Blue Bloods' governing body. She is shocked to find Kingsley Martin seated next to Lawrence. Kingsley, previously exposed as a conspirator aligned with the Silver Bloods (corrupted vampires who prey on their own kind), has been reinstated as a Venator, a member of the vampire secret police. He reports cracks in Corcovado's foundation, disappearances of Elders in South America, and signs of a possible infractio, a breach in the site's seal.
Meanwhile, Bliss experiences terrifying visions of apocalyptic violence. A handsome man in a white suit with golden hair appears and calls her his daughter. Privately, Bliss harbors secrets: Dylan Ward, a Blue Blood classmate everyone believed dead, has returned and hides at the Chelsea Hotel, behaving erratically; and a photograph suggests Schuyler's comatose mother, Allegra Van Alen, may be Bliss's birth mother.
Dylan attacks Schuyler at a secret hideaway on Perry Street using the Consummo Alienari, a devastating mind-control technique. Schuyler nearly kills him before Oliver and Bliss intervene. Dylan reveals he was captured by people he believed were Venators who told him Schuyler was behind recent attacks on Blue Bloods. Schuyler proves her innocence with the mark of the Archangel on her wrist, a sigil identifying her as a Daughter of the Light, and Oliver deduces that Dylan's rescuers were Silver Bloods who manipulated him.
Schuyler and Jack Force, Mimi's twin brother and the angel Abbadon, conduct a secret love affair, meeting at the Perry Street apartment while Jack maintains cold indifference toward Schuyler in public. Mimi discovers the affair and confronts Schuyler, explaining that twins share a bond, a celestial soul-union they must renew each cycle to maintain their full strength and memories. Without renewal, Jack will diminish over centuries, just as Allegra was destroyed when she broke her own bond with Charles.
During a fashion show, Schuyler receives a savage telepathic intrusion and flees to Lawrence, who is packing for Rio. He explains that Corcovado is a place of primal power from which vampires draw their immortal strength, and the earthquake there demands investigation. He refuses to let Schuyler accompany him, saying he must keep her safe as a promise to her mother.
Dylan's condition worsens. He appears raving at the school gates, and Bliss subdues him using the mutatio, the ability to shape-shift. They turn Dylan over to Bliss's father, Senator Forsyth Llewellyn, the acting Conclave head, who places him at Transitions, a rehabilitation center for troubled Blue Bloods. When they later visit, Dylan is pleasant but completely amnesiac. A subsequent visit reveals his doctor found no Silver Blood corruption in Dylan's blood, proving him innocent of the murder of Aggie Carondolet, whose death Dylan had been blamed for. Forsyth knew these results but concealed them from the Conclave.
At a Committee lecture on bonds, Jack telepathically tells Schuyler there is a way to break the bond. He takes her to Vienna, insisting he will risk everything. But when Schuyler privately asks Lawrence, he confirms there is no safe way: Jack would face execution, or his spirit would slowly diminish. Schuyler realizes Mimi told the truth and resolves to end the relationship to protect Jack.
Charles discovers that Michael's sword, the Blade of Justice, the only weapon capable of killing the Dark Prince, Lucifer, has been stolen. Mimi deliberately reveals Schuyler and Jack's affair to Oliver, who confronts Schuyler, accusing her of selfishness for permanently binding his affection through the Sacred Kiss so he can never love another.
When the Conclave is summoned to Rio because Lawrence is reportedly in danger, Schuyler flies there, with Oliver following. They discover Lawrence is fine and never summoned the Conclave; Schuyler's telepathic messages to him were somehow blocked. Lawrence explains that Corcovado is the prison of Leviathan, a mighty Silver Blood and Lucifer's brother, imprisoned beneath the Christ the Redeemer statue by Gabrielle (Allegra) herself.
In Rio, Bliss's younger sister Jordan Llewellyn attacks Bliss with a golden blade, but the emerald necklace Bliss wears, Lucifer's Bane, protects her. Forsyth and BobiAnne, Bliss's stepmother, subdue Jordan. Jordan is revealed to be Pistis Sophia, the Watcher, a guardian spirit Cordelia placed in the family as a safeguard against darkness. Forsyth, BobiAnne, and Warden Nan Cutler, a Blue Blood official, conspire against the Watcher, and Jordan's weapon is revealed to be the stolen Blade of Justice.
The Conclave is massacred at a dinner hosted by the Almeida family, exposed as Silver Bloods. Nan Cutler is revealed as a traitor. Mimi fights free, killing Nan in a sword duel. Only Mimi and Forsyth survive among the Elders.
Lawrence races to Corcovado with Schuyler and Oliver. At the summit, Lawrence duels a man in a white suit, and his blade strikes the figure's chest. The statue of Christ the Redeemer shatters, and Leviathan bursts free, pinning Lawrence with a poisoned spear carrying black fire, which corrodes vampire blood and causes true death. The man transforms back into Dylan, an innocent Blue Blood possessed through the alienari and disguised as Lucifer so that Lawrence would kill one of his own kind, the one act that could shatter Leviathan's prison. With his dying thoughts, Lawrence tells Schuyler to ask Charles about cryptic clues: "the Gates," "the Van Alen Legacy," and "the Paths of the Dead." He reveals that Schuyler has a sister who will be their death, but Schuyler herself is their salvation.
The central mystery resolves when Bliss's memories return. She is the vessel of Lucifer, who has hidden within her consciousness across cycles. During her blackouts, Lucifer controlled her body to kill Aggie, attack Schuyler, and wound Cordelia. Forsyth has always known. The voice of Bliss protests within, but Lucifer commands her to rejoin her friends and bide her time. Bliss climbs Corcovado, finds Schuyler and Oliver with the bodies of Lawrence and Dylan, and claims her sister and stepmother are dead. She cradles Dylan and carries him down the mountain.
In the epilogue, Mimi confronts Jack at the Perry Street apartment after Schuyler has ended their relationship. Jack erupts in rage, and the twins battle before the fight transforms into a fierce consummation of their bond. Mimi reflects that the Conclave is destroyed, the Dark Prince ascendant, and Charles broken. She smooths Jack's hair as he sleeps, believing he will one day thank her for saving his life.