Valkyr, who goes by “Kyr,” runs a simulation called Doomsday on the agoge, a virtual-reality system and a parallel-universe generator. She is in a war that occurred before she was born and is trying to prevent the majo (aliens) from destroying the Earth. Kyr uses a jump hook to navigate through shadowspace and gets on a spaceship carrying a bomb. She tries to disable the bomb, but the technology called the Wisdom stops her. She is shot in the simulation. Fourteen billion people on Earth die. This simulation is based on real events and programmed by Kyr’s uncle Commander Aulus Jole, who was there when Earth was destroyed.

Jole comes into the agoge, tells her that she did a good job, and jokes that she is training in the agoge more than he is. Kyr is upset that she failed. Jole puts a hand on her shoulder, tells her that he’s proud of her, and sends her on a recreation rotation.

Outside the agoge room, Kyr runs into Cleo, her nemesis. They both belong to a mess (a group of young people in training) called Sparrow. Cleo wants Kyr to ask Jole about their assignments. They argue about Kyr’s special treatment from Jole. Cleo calls Kyr ignorant, swears at her, and leaves.

Kyr goes to Agricole, a forest that supplies Gaea Station with food and air. She finds her twin, Magnus, usually called “Mags,” sleeping in the canopy. When she calls him lazy, he replies that he’s on rec rotation. When Kyr starts crying, Mags hugs her. Kyr admits that she couldn’t beat the Doomsday scenario and asks Mags how he beat it. Mags says that Avi, who works in Systems Wing, talked him through the simulation; they beat it together. Kyr considers this cheating. Mags says that the Wisdom cheats, so they should be able to do so as well.

Kyr leaves Agricole and thinks about how she can make it across the station, from Suntracker to Drill, in four minutes and 55 seconds. She has already beaten the records of the fastest boys in Mags’s mess, Coyote. (A “mess” is akin to a class or grade, and each is named for an animal). Kyr goes to the kitchen in Oikos Wing. Younger children from the Blackbird mess are playing with spilled water. Kyr reprimands them because water is limited on the station. She makes one girl drink the water she spilled on the floor.

The other teenagers in Sparrow are Cleo, Jeanne, Zen, Vic, Arti, and Lisbel. Kyr is possessive of and hard on the others. She makes sure that they get high scores and believes that Command will assign them to the correct wings. Jeanne doesn’t come to Oikos because she was assigned to Ferox, a combat wing. Kyr pours drinks, and they toast the Ferox toast, “Fortune favors the bold” (21).

The girls talk about where they want to be assigned. The four combat wings—Ferox, Scythica, Augusta, and Victrix—offer the most privileges. Oikos, Systems, Suntracker, and Agricole keep the station running. Vic is obsessed with Suntracker; Arti wants Scythica. They are a lesbian couple, and same-sex couples are forbidden on the station, but Kyr doesn’t report them. Finally, there is Nursery Wing, where women bear and raise children. Kyr is sure that Lisabel will be assigned there. Cleo and Kyr argue. Lisabel reassures Cleo that she will go to a combat wing. Cleo fears being assigned to Strike, a clandestine wing where humans are sent to sacrifice themselves in terrorist acts. She hopes that Kyr will be sent there instead, but Kyr doesn’t believe Strike exists.

A messenger comes and tells Sparrow that Sergeant Harriman has ordered them to Victrix. There, they are instructed to strip a majo ship, catalog its contents, and pack them up. The majo are a group of intelligent, non-human species occupying many planets throughout the universe. The ship is large and colorful. Other soldiers have handcuffed the ship’s majo owner to the ship because the vessel is programmed to explode if its owner is killed. Guards physically abuse the majo for talking too much, and Kyr suggests that they gag the majo. The ship’s defenses push Kyr away forcefully; the majo was trying to warn her.

The ship is filled with fine clothes and other luxurious items. Kyr kicks the majo for not looking upset that they are tearing apart the clothes for fabric. Another messenger comes and gives Lisabel her assignment: Nursery. Kyr gets a flask from a soldier and uses the alien’s fancy glassware to toast Lisabel. The Nursery toast is “I would rather stand three times in the battle line than give birth to one child” (30)—a line from Euripides’ Medea (also used as the novel’s epigraph). The alien tells them that the glasses are valuable. Kyr and the other Sparrows break their glasses after finishing their drinks. This scares the alien.

Arti is assigned to Augusta and immediately sent on a mission. This upsets Vic, but she is assigned to Suntracker, which cheers her up. The remaining Sparrows work in Oikos while awaiting their assignments. The majo fabrics are used to mend uniforms. When Zen is assigned to Oikos, she tells Cleo and Kyr that she never liked them and leaves them alone together. Either Cleo or Kyr will have to be assigned to Nursery to keep up the population targets.

Kyr doesn’t want to be assigned to Nursery and give birth every two years. Nursery Corporal Ekker, who raised Kyr, recently died, and Kyr only vaguely remembers her. Mags and Kyr were born after their parents were dead by using their genetic material. Their father worked with Jole, and their mother worked on Victrix. Their sister, Ursa, was born before their parents died; she was conceived the “old-fashioned way” (36).

The next day, there are no assignments for Cleo or Kyr. Kyr says that they must be on a rec rotation. They go to Drill and fight in various matches. When other messes come through Drill, they watch Cleo and Kyr. After the crowd says some offensive things that Kyr ignores, Cleo says she’s done fighting. They go back to their barracks. Cleo is upset that they still don’t have assignments. Kyr decides to ask Jole about it.

Kyr has access to Jole’s quarters and lets herself inside. He isn’t there, so she waits for him. She remembers how Ursa used to sleep on a cot in Jole’s quarters. Most people on the station don’t have a family like Kyr. Jole returns, with his gun pointed into the room, but lowers it when he sees Kyr. Kyr asks about the assignments, and Jole gives her the flimsies (similar to floppy disks) containing them.

She expresses shock at finding that she is assigned to Nursery, and Jole explains: Her top scores mean that she can birth good soldiers. He picked her for Nursery because she is good at combat. Kyr complains but accepts the assignment. She can’t bring herself to ask about Mags’s assignment. Jole says that Kyr is on rec rotation for the rest of the day and will report to Nursery tomorrow. He also says he’s proud of her.

Kyr is in shock when she leaves Jole’s quarters. She fights nausea and dizziness by stretching. Then, she opens Cleo’s assignment, which is to Victrix. Kyr considers running the Doomsday simulation again and gets upset knowing she won’t be able to train while working in Nursery. She goes back to the barracks and gives Cleo her assignment. Kyr lies and says that she hasn’t been assigned yet. Though they have neither glasses nor alcohol, they say the Victrix toast: “Victory or death” (49).

Cleo confesses that she and the others hate Kyr because she consistently beats them in the station’s many formal and informal contests for the approval of those in power. Cleo hopes that Kyr is assigned to Strike and dies. Kyr resists reacting, and Cleo leaves. Kyr remembers when Jeanne, Arti, and Cleo demanded that Kyr stop making Lisabel do extra drills. Then, Kyr goes to Nursery and visits with Lisabel. Lisabel makes Kyr some tea and asks if she’s okay after what happened with Mags. Kyr doesn’t know what Lisabel is talking about.

Lisabel explains that she heard Mags was assigned to Ferox but turned down the assignment. He was then offered a place in any other combat wing, but he refused again and left the station. Kyr says that it’s just a rumor, and Lisabel says Kyr is probably right. Internally, Kyr thinks it makes sense that she was assigned to Nursery if Mags isn’t part of the fighting force; they need more boys like Mags. People are saying that Mags is being manipulated by Ursa. Lisabel holds Kyr’s hand, and Kyr tells her not to worry.

As Kyr is about to leave, Admiral Russell comes into Nursery, flirts with Lisabel, and dismisses Kyr. Kyr mentally vows to break Russell’s hand if he ever touches her. Then, she thinks about how Mags cheated at the Doomsday simulation.

Kyr goes to Systems Wing, and Corporal Lin tells Kyr that Avi is in the arcade. There, the Blackbird mess is playing a dancing game. Kyr finds Avi slouched in a booth watching something. When he ignores her, Kyr turns off the screen he’s watching. Kyr demands that Avi help her find Mags. He says that he doesn’t want to get executed for helping her, but he eventually agrees.

Avi and Kyr go to the agoge. Kyr worries that someone will check the logs, so Avi gives her a simulation to run, as well as an earpiece, and stays outside. She fights enemies she doesn’t recognize. Avi tells her that they’re orcs from a book. Kyr climbs a building and hides on a rooftop. Avi tells her to look for a weapon, and she finds a staff. When the orcs find the stairs and make it to the roof, Kyr fights them with the staff. Avi says that she’s using the weapon wrong; it’s a wizard’s magical staff that can cast spells. She kills the orcs without magic.

The simulation ends, and Avi is still looking online for Mags’s records. Kyr asks for a simulation that Avi made for Mags. It is a beautiful cliffside garden with colorful plants she doesn’t recognize; they aren’t the edible plants from Agricole. There are no enemies for her to fight. She looks at a fountain, off the cliff, and at the sky when the sun starts to set. After she relaxes for a while, Avi announces that he’s found Mags.

Avi comes into the agoge and summons controls. He tricks the logs into displaying Kyr running a simulation. Then, he explains that the agoge’s shadowspace technology comes from majo technology. Kyr suspects that Avi admires the majo, but he is deeply angry that they destroyed Earth. He displays Mags’s Command file: It says that Mags refused his assignment and left the station. Avi doesn’t believe that Mags would leave Kyr behind.

Avi says that they’ll get caught the “next time Lin does a security sweep” if he keeps digging (74). Kyr tells him to go ahead. Avi projects a broadcast by Ari Shah, a journalist. The story is about the Prince of the Wisdom. Ari interviews Professor Hussain, who explains that the prince doesn’t rule the majoda—a loosely aligned group of worlds—and may not know about their connection to the Wisdom at all. The current prince, Leru Ihenni Tan Yi, looks like the alien whose ship Kyr was cleaning out; they are both from the majo zi species. The prince is going to visit Chrysothemis.

Avi stops the recording and explains that there are 2 million humans on Chrysothemis, and Ursa is among them. Mags asked Avi to find Ursa. Mags’s file says that he’s assigned to Strike. Avi and Kyr think that Jole runs Strike. Kyr starts reading the details of Mags’s mission, set to take place when Leru arrives on Chrysothemis, but Avi makes the information disappear. He suggests that Kyr blame him for showing her classified information. She says that she wouldn’t blame him. Kyr is upset that Mags will get killed on this mission and that his target isn’t the prince; it’s the humans who work with the majo.

Kyr decides to go after Mags, prove that she should be in combat, and save his life. Avi disapproves. Kyr tells Avi that she believes he will help save Mags because he loves him. Avi is surprised that his sexuality doesn’t bother Kyr, and he demands that Kyr take him with her. Kyr thinks that he’ll be a liability, but she agrees.

Kyr tells Avi to wait with a grapple in the caves below Suntracker. When he complains, she suggests that they steal a dart instead of the majo ship. Avi says that Ursa only got away with that because she had a hostage. Once inside the tunnels, Kyr tells Avi that she’ll give him a signal to use the grapple to descend to the cavern.

Inside Victrix, she heads to the bridge. With directions from Avi, she turns on auxiliary power. Kyr touches a distress signal on the console, and a message from Admiral Elora Marston plays. She is fighting against the rebels trying to take over her ship. Kyr has never heard of a woman climbing the military ladder higher than the rank of sergeant. However, Kyr recognizes her name as the name of Jole’s late wife and her own genetic mother. Avi directs Kyr to do things on the console that she doesn’t understand, and she heads toward the brig.

She tells the guard there that she has a message for him. She hands him the flimsy with her assignment to Nursery, and when he opens it, she chokes him until he is unconscious. She takes back the flimsy, as well as his knife, gun, and old-school Victrix insignia. Avi turns the brig power off long enough for her to open the door to the majo’s cell. The majo asks why she is afraid of them. She undoes their bonds and tells them to get up. They say that they don’t want to die, and she pulls them to their feet.

When they resist, she holds their wrist and has a vision of killing the guard, rather than knocking him unconscious. The majo pulls their hand away. Avi tells Kyr to be nice in her earpiece. She assures the majo that she is there to rescue them. When they leave, she checks if the guard is still alive, and he is.

The majo introduces themself as Yiso. They annoy Kyr by talking too much. When Yiso and Kyr get to the hangar, Kyr signals for Avi to jump with the grapple. Yiso can’t keep up, so Kyr carries them while running. Alarms start to sound, and Kyr waits for Avi. He appears, with his hands on his head, led by Cleo. She makes him kneel and threatens Kyr. Kyr and Cleo fight, and Kyr tells Avi to get on the ship. Cleo shoots at Kyr but misses. Kyr gets the gun away from her, and they wrestle.

They pull out their knives. Cleo condemns Kyr for running away and cuts her arm shallowly. Kyr says that Cleo is her sister, and Cleo says Kyr’s a traitor. Kyr says that she’s going to help Mags, and Avi yells for Kyr to get on the ship. Kyr has never killed anyone and can’t kill Cleo. Cleo stabs Kyr in the thigh. Yiso pulls Kyr into the ship with the Wisdom’s reality-bending technology. Yiso worries about Kyr’s injury. Avi says that they need to get out of range of Gaea Station before doing first aid. Yiso thanks Kyr for saving them, and Kyr passes out.