As they descend into the tomb, Hazel guides them through ominous tunnels lined with death masks; the masks’ agonized expressions make Apollo realize that the death masks are really cruel trophies of those the king has murdered. The group presses on, bypassing several traps thanks to Hazel’s direction. When two skeletal guards block the way ahead, Hazel uses her powers to psychically order them to stand down. The path is now clear to Tarquin’s throne room.

From a balcony, they see Tarquin—a skeleton animated by purple gas. The undead king is attended by equally undead servants. An aide (a eurynomos name Caelius) reports that an enemy fleet will arrive in three days. He cryptically comments that a “silent one” is guarded at Sutro Tower. Tarquin plans to invade the city on the night of the blood moon, while the heroes of Camp Jupiter are distracted by the emperors’ attack from the sea. At one point, Lavinia is horrified to recognize a zombified legionnaire, Bobby, among the undead. Suddenly, Tarquin senses their presence and orders the four questers to come down and face him.

Rather than obeying the general group consensus to retreat, Meg rashly attacks Tarquin’s minions, and her companions join the fight. Apollo’s divine archery skill briefly returns, and a grief-stricken Lavinia destroys the zombified Bobby. However, Tarquin repels Meg and Hazel with an invisible force, then magically aggravates Apollo’s wound, revealing that the scratch on Apollo’s belly contains a poison that will slowly turn him into one of the undead. Tarquin is delighted that Apollo has come to face him, as his close proximity has allowed Tarquin to accelerate the poison’s progress. Tarquin also mentions that he is currently holding a Sibyl captive.

With a supreme effort of will, Hazel collapses the stone ceiling on Tarquin, covering him in rubble and allowing them to retreat. However, her attack is a temporary measure and does not annihilate the undead king. As more of the undead pursue them, Meg creates a chute of tree roots to carry the questers up to the surface. To help them escape, Lavinia acts as a decoy and draws the monsters away while the others support a swooning Apollo and attempt to flee.

Apollo has a dream of the monstrous Python taunting him, then awakens then next day to find himself lying in the camp stables. The head healer, Pranjal, treats his wound with unicorn horn shavings but explains that this remedy will only slow the infection; a permanent cure requires divine healing. The conversation also makes Apollo awkward when he realizes that Pranjal (the son of Asclepius) is effectively his grandson. When Apollo asks, Meg confirms that Lavinia has returned safely.

Later, Reyna and Frank announce the discovery of a new prophecy for a ritual to summon divine aid. Reyna states that the ritual “requires the death of a god” (179).

Reyna reads the full ritual instructions. The ritual itself calls for the “last breath of a god who speaks not,” and it must be performed on the “day of greatest need” (181). Then the supplicant must deliver a prayer made “through the rainbow” (181). Apollo realizes that this line refers to an Iris-message (a message sent through the goddess of the rainbow). He also deduces that a “soundless god” would be capable of blocking the camp’s magical communications. He concludes that in order to complete the ritual, they must find and kill this god, who is being held captive at Sutro Tower.

Frank identifies the “day of greatest need” (181) as April 8, the invasion date. He assigns Apollo, Meg, and Reyna to the quest. Frank will remain to lead the camp’s defenses.

That evening, Meg explains that in the tomb, she attacked Tarquin because she hoped that annihilating the undead king would break the poison’s hold on Apollo. Hearing this, Apollo realizes how deeply Meg cares for him, and he realizes that he feels the same way about her. In a rare tender moment, he hugs her as she cries. Later, Apollo dreams of Caligula and Commodus test-firing a Greek fire mortar from their yacht; the fleet of yachts carries 50 such weapons. He wakes to find that his wound has worsened, so he selects clothing that will hide the evidence of his growing infection and keep his friends from worrying.

At lunch, Lavinia asks Apollo about her divine mother’s magical dancing shoes, which Caligula has aboard his yacht. Apollo tries to discourage Lavinia from storming the emperors’ fleet of yachts in order to recover her mother’s shoes. As talk turns to more immediate matters, Apollo warns the Fifth Cohort about the Greek fire mortars. To prepare the legion for the invasion, Frank announces that war games will begin immediately.

The day before the battle, Apollo is tasked with teaching archery lessons while Meg focuses on “weaponizing” the resident unicorns. He is pleased to realize that his divine archery skills have returned permanently, and he spends the afternoon coaching the legion and boosting morale.

After training, Lavinia and Don the faun intercept Apollo, urgently asking for his help, but they refuse to explain until they are out of the camp altogether. He agrees to help them slip out of camp for an unauthorized mission.

That night, Lavinia and Don take Apollo to a gathering of fauns and dryads in Berkeley’s People’s Park. There, he spots Meg’s karpos (tree spirit), who is named Peaches and can only communicate by repeating his name in different tones. (Peaches went missing in the previous installment of the series.) Now, at Lavinia’s request, Apollo sings about the threat of the Greek fire mortars. The fearful nature spirits close ranks and exclude him from their council as they debate how best to fight back against the imminent attack.

Lavinia explains that she has chosen defect from Camp Jupiter and aid the nature spirits instead of fighting with the legion. Apollo returns to camp. Not wanting to distract or upset Meg, he elects not to tell her that he saw Peaches. He retires for the night and wakes on the morning of April 8, the day of the battle.