Planesrunner

While the Everness crew assess their location and the condition of the airship, Everett tries to figure out how to interface the Infundibulum with Charlotte's jumpgun so he can choose the destination planes of future jumps. Something large appears on the radar, headed their way: a massive hovercraft battleship, with insignia that identifies the Islamic Britain of E2. It is swallowed by a giant creature that breaks through the ice just as the Everness jumps to Everett's home plane, E10. Meanwhile, an alternate Everett in E4—whose father Tejendra was previously hit by a truck on his bicycle and killed—is hit by a car himself. He awakens in a station on the Moon, where an alien machine intelligence known as the Thryn arrived in 1963. Kept secret from the majority of people on Earth for 20 years, the Thryn Sentiency helped mankind achieve important medical and technological advancements, including the creation of the Heisenberg Gate. Plenipotentiary Charles Villiers—Charlotte's E4 counterpart—asks E4 Everett to become an agent for the Plenitude. The Thryn avatar Madam Moon rebuilds Everett's wrecked body with technology that provides enhanced strength, speed, and agility; heightened senses; and built-in weaponry. He goes to E10 Everett's home, impersonates him, and attacks when E10 Everett arrives to rescue his mother and sister.

The Everness escapes to the quarantined plane E1, where E10 Everett believes the jumpgun was created. He hopes to learn how to track past jumps in order to find his father. E1 has been overrun by a nanotechnology breakthrough gone awry, known as the Nahn, which has already assimilated six billion people and seeks to supplant every living thing on the planet. Sixsmyth and the crew are taken into custody by the government force protecting the few survivors in London, led by a politician called the Agister of Caiaophas and her military commander, the Brigadier. They hope to escape E1 with their people using the jumpgun and the Infundibulum. E10 Everett meets the E1 Tejendra, who guides a strike team to the Nahn-infested remains of Imperial University in search of a device used in a 1969 E1 survey to map thousands of planes. Tejendra is assimilated during their frantic escape back to the Everness with the device, and Everett opens a Heisenberg Gate tuned to the center of a sun that incinerates the whole of the university and the Nahn. Seeing the power of Everett's "sun gun", the Agister decides to stay and use it to rid E1 of the Nahn. The Everness crew depart, with the Panopticon mapping device, to find Everett's father, the E10 Tejendra. Meanwhile, the Villiers send E4 Everett to E1 in Thryn battle armor to attach a tracking device to the Everness. Though outfitted with weaponry designed to neutralize the Nahn, he is overcome by them. E4 Everett makes a deal: in exchange for his life, he agrees to carry some of the Nahn out of E1. Successfully attaching the tracker, he is jumped out by the Villiers, who place him back with E10 Everett's mother and are unaware that he carries a node of the Nahn.

Kirkus Reviews called Be My Enemy "smart, clever and abundantly original, with suspense that grabs your eyeballs".[7] Stefan Raets of Tor.com called the novel "outstanding" and "a blast from start to finish", but found some plot points lacking.[10]

The Everness is forced to make a random jump, and the airship is seriously damaged by its arrival in the middle of a jungle. Everett soon realizes that this "Earth" is actually an Alderson disk, so his navigation calculations were off. Determining that humans could not be advanced enough to construct the disk, he theorizes that dinosaurs who have evolved over 65 million of years might be capable. This is proven true when just such a dinosaur, Kaz, approaches Everett and is able to learn the English language almost instantly with advanced technology. The Worldwheel is ruled by six factions, or clades, each responsible for a key function: water, weather, agriculture, procreation, defense, and the sun itself. With Everett's help, Kaz defeats her rival and secures her position as heir to the Sun Throne of the Sunlords. Meanwhile, Charlotte Villiers is still hunting the Everness and the Infundibulum. She leads a strike squad into the airship expecting to face only the crew, but the Genequeen clade of Jiju attack the Everness as well, forcing Charlotte to flee and leave her team to be massacred.

E4 Everett begins to settle into the life of his E10 counterpart after destroying the Nahn he brought with him from E1. Though he hides his Thryn abilities as best he can, some of the changes do not go unnoticed, giving Everett a bevy of female admirers and ultimately forcing him to admit to E10 Everett's best friend Ryun that he is E4 Everett. On the Worldwheel, Kaz brings E10 Everett and Sharkey to the Sunlord capital to meet her mother, the Empress of the Sun. After copying the Infundibulum, the Empress uses it to begin an invasion of billions of planes in the extended multiverse, and prompts the Worldwheel's sun to go nova, sanitizing the world and exterminating all of the other clades. The Everness escapes just in time. E10 Everett has a plan: since the Empress copied the Infundibulum exactly, Everett can control it with his smartphone. With Kaz's help, the airship crew infiltrates the Empress's city-ship over E10 London, and Everett sends a signal that jumps all of the Jiju ships into random planes, and then erases all copies of the Infundibulum. Charlotte returns to her true home plane, which she has dubbed E3A. She longs to be reunited with her lover Langdon, who is trapped in the rift between planes after going through an early iteration of the Heisenberg Gate.

Kirkus Reviews described Empress of the Sun as "endlessly fascinating and fun."[11] Stefan Raets of Tor.com deemed it the best novel in the series so far, and praised its dynamic characters.[12]