On Christmas Eve, to "make everything right," Julius Kane releases Osiris from the Rosetta Stone with the intention of hosting him and then dying in order to return him to his rightful throne in the Duat and take the first steps towards restoring Ma'at. However, he also releases Horus, Isis, Nephthys and Set unintentionally. Horus takes Carter Kane as a host, Isis takes Sadie Kane, Nephthys takes Zia Rashid and Set takes Amos Kane. Set takes Julius/Osiris prisoner in a sarcophagus he makes and starts building his Red Pyramid in Camelback Mountain near Phoneix, Arizona with the plan to create the greatest storm ever, augmented by Osiris' power on his birthday, December 29 which will destroy the North American continent and make him invincible. Later, at the suggestion of his demon minion Face of Horror, Set uses Amos Kane to lure Carter and Sadie into a trap to use the powers of Horus and Isis to further augment the storm.
Attack on the Pyramid
Possessing Amos, Set successfully leads Carter, Sadie and Zia Rashid to the red pyramid where they find the pyramid nearly complete with all that's left being the pyramidion. In order to stop it, Carter, in the form of a falcon, Sadie, in the form of a kite, Amos/Set, in the form of a fruit bat and Zia, hanging onto a giant vulture transformed from an amulet, fly to one of the two boats carrying the pyramidion and kill the demons there. Amos/Set then turns the other boat to smoke, causing all of the demons on it to fall to the ground. Carter cuts the lines from their boat holding up the pyramidion and it falls, crushing many demons. However, the rest start attacking the boat, so Amos/Set sets it on fire and crashes it into the demon ranks as a distraction while the others fly away. Upon reaching the pyramid, Carter seals the doors with an Eye of Horus and they travel to the throne room where they find Osiris' coffin and Set arrives in the form of Amos and reveals his possession of Amos to the group, abandoning Amos' body as he no longer needs it.
Battle while in Phoenix
Carter attacks Set to no avail and is pinned to a wall while Set goes after Zia, believing her to be hosting Nephthys, not knowing she is actually a shabti. Upon discovering the truth, he throws her into a pillar, badly injuring her and Carter, enraged, merges with Horus to become a perfect union of the god and human. The two battle, but after realizing that the throne room is collapsing from the battle, Carter turns Set into a fruit bat and himself into a falcon and flies out through an air shaft to continue the battle on the outside of the pyramid. There, he discovers an army of magicians from the House of Life led by Michel Desjardins fighting a losing battle with the demon army and having no effect with their attacks on the pyramid. Four giant, snake-headed demons, under the command of Face of Horror work to bring the pyramidion into position and Set keeps Carter from interfering. However, Desjardins blows the demons away and attempts to destroy the pyramidion, but fails and is knocked out by Set. Carter charges Set again and they battle, but Carter is unable to defeat Set and Set uses a moment of distraction to knock Carter down. Set then places the pyramidion in place himself with just thirty seconds to sunrise at which point he will unleash his storm and destroy North America. However, Sadie, now merged with Isis and having learned Set's Secret Name from Nephthys through Zia, arrives on top of the pyramid and opens a portal that swallows the pyramid, Set, Set's army, the magicians, herself and Carter, transporting them to by the Washington Monument in Washington, DC and cutting Set off from the source of his power, the desert.
Battle while in Washington DC
Traveling to Washington, DC knocks out the magicians and any mortals nearby, but the Monument re-energizes Carter while being cut-off from the desert weakens Set. With Set weakened, Carter is able to easily hold him off, allowing Sadie to cast the banishing spell from the Book of Overcoming Set The spell opens a rift to the Duat that the demons are sucked into and destroys the Red Pyramid as well as bonding Set in white energy once Sadie says his secret name. However, before she can finish the spell, she notices a snake in the clouds that planned to use the chaos energy generated by the destruction of North America to escape its prison and she realizes who it is: Apophis. Sadie stops the spell, realizing that Apophis has been the one truly behind everything and uses the Feather of Truth to show everyone Apophis in the sky. Face of Horror, revealed to be possessed by Apophis, tries to kill Sadie, but Carter throws his khopesh into the demon's side, killing him. Sadie disperses Apophis with a burst of wind and the rift closes. Sadie and Carter then make a deal with Set: in exchange for letting him go, he will leave for the Duat and only return to fight Apophis when they call upon him. Set swears to do so on his secret name, the throne of Ra and Nut's starry elbows. Once the deal is made, Sadie orders him to leave and Set leaves for the Duat.
Carter and Sadie find Amos and Zia both still alive due to Zia casting a shield over them before the pyramid was destroyed. However, Osiris and Julius Kane aren't saved and both Amos and Zia are in bad shape: Amos nearly burned his soul out during Set's possession and Zia used up all of her remaining energy to shield them. Zia dies, but as she's a shabti, she merley crumbles to dust and sends her memories to the real hidden Zia, asking Carter to find the real one before she dies. Carter vows to find the real Zia and Carter and Sadie are confronted by Desjardins and four other magicians who are displeased that they made a deal with Set rather than banishing him. Carter and Sadie have Horus and Isis leave them, but decide to teach the Path of the Gods in order to be able to face Apophis once he eventually breaks free. While Desjardins is against this, he leaves them alone, saying enough destruction had been wrought for one day, but warning them not to teach the path as there would be consequences. Turning into their bird forms and Amos into a hamster, Carter and Sadie escape the scene before the mortal authorities arrive and make their way back to Brooklyn House. There, Amos falls into a depression from his possession by Set, but eventually recovers with the help of healers from the First Nome.