Sentinel (covenant, #5)

The fifth and final installment in the Covenant series takes place in a world where descendants of the Greek gods live in hidden communities called Covenants. Pure-bloods hold power over half-bloods, who are forced into roles as Sentinels (warriors who hunt daimons, aether-draining creatures), Guards, or servants. The Apollyon is a demigod warrior born once a generation who wields all five elements, including akasha, a destructive force normally reserved for the gods. When two Apollyons exist simultaneously, one can transfer power to the other, creating the God Killer, a being capable of slaying an Olympian.

Alex Andros, the Second Apollyon, regains consciousness at the University, a Covenant campus in South Dakota, her body covered in scars from her battle with Ares, the God of War. The sun god Apollo had briefly transported her to Olympus for healing before returning her to the University. Aiden St. Delphi, Alex's pure-blood boyfriend, recoils when her eyes open: They glow amber, identical to those of Seth, the First Apollyon, raising the fear that Seth has regained control over her. Alex reassures Aiden otherwise, but she discovers a hand-shaped scar on her lower back that she hides from him. More troubling is a deep emotional numbness. She can feel fear and anger, but grief, love, and tenderness are muted, as though sealed behind glass.

Alex gathers with allies including Marcus, her uncle; Olivia and Luke, half-blood Sentinels; Solos, a half-blood warrior; and Diana, a Head Minister on the Covenant's governing Council. News broadcasts reveal wars erupting across the Middle East, fueled by Ares, and the group recognizes he intends to subjugate humanity. At a funeral for those killed in the attack, Alex's grief remains muted. She confesses to Aiden that she cannot feel anything except fear and pain. He reassures her she is not broken.

The University comes under attack by daimon-possessed birds and a horde of daimons. Alex draws her daggers but freezes, hallucinating Ares's face on an approaching daimon. Artemis, Apollo's twin sister, materializes to help and warns that Seth is heading toward the University. She touches Alex and declares something is inside her. Alex breaks free only when she sees Aiden bitten by a daimon; protective fury overrides the fear. That evening, Aiden suggests what Artemis sensed could mean Alex is pregnant. Alex cannot rule it out.

During Alex's recruitment speech, the psychic cord between her and Seth flares to life. She races to the gate, where Seth kneels with hundreds of loyal Sentinels and surrenders, apologizing through their mental bond. Seth has brought Lucian, Alex's pure-blood stepfather and the man who corrupted Seth, under compulsion, revealing that Lucian knew of Ares's plan and laughed. Alex draws her gun and shoots Lucian in the forehead without hesitation. Aiden knocks Seth unconscious, and Seth is locked in a titanium cell.

Later, Alex hallucinates Ares's face replacing Aiden's mid-kiss and pulls a gun on him. Aiden talks her down. Unable to sleep, she visits Seth's cell, where he proposes transferring his power to Alex so she can become the God Killer and reveals her father is alive at the Catskills Covenant. Aiden discovers the visit and overhears Alex admit she wanted to die during the fight with Ares. Deeply hurt that Alex confided in Seth rather than him, Aiden walks away.

Apollo arrives and examines Alex, discovering the hand-shaped mark. Ares branded her during the fight, giving his twin sons Phobos and Deimos, the Gods of Fear and Terror, access to her psyche. Apollo commands them out; two pillars of smoke pour from Alex's mouth and vanish. The twin gods had been amplifying fear and pain while suppressing every other emotion, explaining the numbness, the hallucinations, and Alex's inability to grieve. The pregnancy is never real; the twin gods are what Artemis sensed. The revelation triggers a volcanic release: Alex's suppressed grief erupts, and she destroys a room with akasha. Seth lets her strike him until she collapses sobbing. Afterward, Alex and Aiden reconcile.

Apollo confirms Seth has genuinely turned against Ares. Athena, the Goddess of Wisdom, proposes releasing Perses, the Titan God of Destruction, from Tartarus to train Alex and rattle Ares, who nearly died fighting Perses in the ancient Titan war. Hades, god of the Underworld, agrees but demands Aiden's soul: When Aiden dies, his soul will belong to Hades, barring him from the Elysian Fields, the Underworld's paradise, forever. Alex protests, but Aiden accepts. Alex leverages her own indispensability, demanding that Apollo free all half-bloods from the Elixir, a potion that suppresses the will of half-blood servants, abolish forced servitude, and grant them equal rights. Apollo agrees.

Hades teleports Alex, Aiden, and Seth to the Underworld, where they awaken Perses. Back at the University, the Titan begins brutal combat training. After days of failure, Alex blasts Perses with akasha and takes him down, the first to defeat the Titan. She convinces Aiden to stay with the main army during the final battle. Seth refuses to transfer his power until they reach the Catskills, admitting he is not certain he can resist taking it for himself.

The army departs for New York. Near the Catskills, the convoy is ambushed by Spartoi, warriors born of soil who are sons of Ares, and automatons. A Spartoi's ax strikes Olivia; a red film envelops her and she vanishes. At the base camp, Alex's father appears. He communicates through a notepad because Head Minister Telly cut out his tongue years earlier. He writes that he is proud of Alex, meets Aiden, and returns to protect servants trapped inside the Covenant.

At dusk, the army launches its assault. Alex, Seth, and Perses infiltrate through the eastern wall while Aiden leads the main force at the front gate. Nine Olympian gods materialize on the battlefield; Apollo has rallied them. Inside the Covenant, Perses vanishes, reappearing in the ballroom confronting Ares. Seth tells Alex it is time. She performs the ritual, speaking four Greek words while touching specific points on Seth's body, and becomes the God Killer. Together they battle Ares. Seth stabs him in the back while Alex unleashes akasha at full force. Seth grabs her hand, amplifying the power through their bond, and the combined blast consumes Ares in white light. A sonic wave follows, knocking Seth unconscious.

The 11 remaining Olympians materialize. Zeus, king of the Olympians, declares that a God Killer cannot exist. Alex looks to Apollo, who shakes his head. Seth erupts in fury, but Alex accepts her fate. She asks Seth to take care of Aiden. Apollo steps forward, and Alex's mortal life ends in a burst of sunlight.

Alex awakens in Hades's palace, healed. Persephone, Hades's wife, escorts her to the Elysian Fields, where Alex wills a paradise into existence: a replica of Aiden's cottage on Deity Island, a Covenant settlement. She reunites with Caleb, her best friend who died earlier in the series, as well as Olivia and her mother, but remains consumed by longing for Aiden.

Apollo visits and reveals the truth. During Alex's earlier stay in Olympus, he secretly gave her ambrosia, the nectar of the gods, making her immortal. Her mortal death activated this gift; she is now a demigod who must spend six months in the Underworld and six months in the mortal realm. Apollo also reveals that Seth independently offered his eternal servitude and agreed to take Aiden's place in Hades's service after death, in exchange for ambrosia for Aiden. Aiden is now immortal, and his soul is free.

Aiden appears on the beach. He takes the Council seat inherited from his late father long enough to vote to abolish the Breed Order, the law mandating half-blood servitude, and to grant half-bloods equal rights, then gives the seat to Solos before accepting ambrosia. Alex and Aiden enter their cottage together, now demigods with an eternity before them.