Starsight recap

Humanity on Detritus now knows that its jailers are the Superiority, a galactic government that grades species by aggression and denies faster-than-light travel to those it judges unfit. When a cytonic alien pilot named Alanik crashes on Detritus and falls into a coma, Spensa takes her ship and her identity and infiltrates a Superiority fighter program on the space platform of Starsight, intending to steal the secret of interstellar travel. Disguised among alien cadets, she learns that the Superiority's hyperdrives are not machines but living creatures, taynix slugs of the same kind as her own Doomslug, and that the program's director, Winzik, does not want to defend anyone from the world-killing entities called delvers so much as to control one. When Winzik draws a delver to Starsight, Spensa flies out and makes contact with it, discovering it is a lonely intelligence rather than a weapon, and persuades it to leave. She escapes with a hoard of taynix, giving humanity hyperdrives at last, while Winzik gains the power he was after.

Previously: the survivors of humanity live in caverns on the planet Detritus, penned beneath a shell of orbiting debris and raided by alien Krell fighters. Spensa Nightshade forced her way into the Defiant Defense Force's pilot training despite her father having been branded a coward for fleeing the Battle of Alta, and secretly rebuilt a wrecked, far more advanced starfighter she found in a cave, whose artificial intelligence calls itself M-Bot. She learned that her father had not fled at all: he was cytonic, one of the rare people who can hear the stars, and Admiral Ironsides shot him down out of fear of what that ability does to a pilot. In the battle for Alta, Spensa used the same ability herself, teleporting above the debris field, and discovered that the Krell fighters were unmanned drones flown by aliens who had been keeping humanity imprisoned and culling it whenever it grew too capable. She destroyed their command ship. Ironsides surrendered command to Cobb, her father was cleared, and Spensa was confirmed as a pilot under the callsign Spin. Humanity now understands that it faces a galactic civilization with vastly superior technology, and that Spensa can partly do what that civilization does.

Detritus is still besieged, but the DDF now fights an enemy it can name. Spensa flies with Skyward Flight, works with the rebuilt M-Bot, and trains a cytonic ability that lets her hear the enemy and, with effort, teleport. Engineers including Rodge are slowly reclaiming the ancient orbital platforms above the planet, but without a hyperdrive humanity cannot leave, and one besieged world will not hold forever. Then an alien starfighter arrives at Detritus and is shot down. Its pilot, Alanik of the UrDail, is cytonic; she came deliberately to find humans, hoping for allies against the galactic government known as the Superiority, and the crash leaves her comatose. Her ship, her equipment and her identity give Spensa an opening. The Superiority is recruiting alien pilots for a new program, Spensa can pass for Alanik with a disguise and a borrowed ship, and so she hyperjumps out alone, intending to infiltrate the Superiority and bring home the secret of faster-than-light travel.

Posing as Alanik, Spensa reaches Starsight, an enormous space platform and one of the Superiority's central worlds, where dozens of species live under a government that ranks civilizations by their supposed primitive aggression and withholds interstellar travel from those it judges unfit. She is accepted into a new fighter program run by Winzik's department, which is quietly recruiting the very species it calls aggressive to do its fighting for it. Her fellow cadets include Morriumur, a dione whose existence is still provisional and who must prove worth being born; Hesho, a kitsen small enough to stand on her hand and until recently the emperor of his people; and Vapor, a cadet with no body at all. Winzik belongs to the same species as the aliens who ran the drones over Detritus, and his staff includes Brade, a human raised inside the Superiority as a servant and a curiosity. Spensa also meets Cuna, a senior official whose interest in her is impossible to read. Her goal throughout is simple: find out how Superiority ships jump between stars, and take that knowledge home.

Training with the flight, Spensa sees how completely the Superiority's citizens have been taught that aggression is a disease and that species like hers are vermin to be contained. She grows genuinely fond of Morriumur, Hesho and Vapor while keeping her identity hidden, and the strain of the disguise increases: she cannot use her cytonic abilities openly, since the Superiority reserves and controls cytonics, and Brade can sense other cytonics. She learns what the program's pilots are actually being prepared for. They are not being trained against the Superiority's rivals but against a delver, an entity that arrives out of nowhere and annihilates whole populations, and against which the Superiority's usual weapons are close to useless. Her investigation of the hyperdrive also begins to yield results, though what she is turning up does not resemble machinery.

The investigation pays off. The Superiority's faster-than-light drives are not machines but living creatures, taynix slugs that can teleport, of the same kind as the yellow slug that adopted Spensa back on Detritus. The Superiority guards this absolutely, because it is the foundation of its control over every other species: grant a world hyperdrives and you no longer own it. Spensa's reading of Winzik's program darkens in step. The pilots are being prepared to face a delver, and she begins to suspect he does not intend to defend anyone from one. Cuna, whom Spensa had taken for an enemy, proves instead to be an opponent of Winzik's faction and a genuine advocate for admitting species like hers to full citizenship. Meanwhile Spensa's cover frays: Brade senses her, and every extra day makes it likelier that the Superiority discovers a human loose on Starsight.

Winzik's plan comes clear. Delvers are drawn by cytonic noise, and his department has learned enough to attract one deliberately. He does not want to protect the Superiority from delvers; he wants to be the only power able to summon and aim one, which would make his faction unassailable and justify permanent emergency authority. Cuna is manoeuvred out of any position to stop him. Spensa's cover collapses and she is exposed as human, which Winzik finds useful rather than inconvenient, since the fear of her species is exactly the argument he has been making. Her friends in the flight are left to choose between what they have been taught about humans and what they have seen of her. And Starsight itself, with millions of people aboard, is where Winzik intends to make his demonstration.

The delver arrives at Starsight and Winzik's forces let it come. Most of the platform's population cannot be evacuated. Spensa flies out to meet the delver and, instead of attacking, reaches for it cytonically. What she finds is not a weapon but something enormous and utterly alone, which hears the minds of living things as unbearable noise and does not understand that the things it silences were people. She shows it what it is doing, and it withdraws. Starsight survives. In the chaos Spensa frees a hoard of taynix from Superiority control and escapes with them, with Doomslug, and with M-Bot, whose ship is destroyed and whose mind continues in a much smaller body. She hyperjumps home to Detritus with faster-than-light travel in the hold, and the orbital platforms are brought online, shielding the planet for the first time. But Winzik has what he wanted: authority, a fleet, and a way to point delvers at his enemies. Alanik has woken on Detritus, Jorgen has begun to show cytonic ability of his own, and the aliens Spensa befriended now know she is human.

Winzik's department draws a delver to Starsight and makes no serious attempt to stop it, intending the destruction as a demonstration of the threat only he can manage. With evacuation impossible for most of the platform's millions, Spensa flies out to meet the delver and uses her cytonic ability to make contact rather than to fight. She finds that a delver is not a weapon but something vast and profoundly alone, which experiences the noise of living minds as pain, and she shows it what it is killing. The delver withdraws and Starsight survives. In the confusion Spensa frees a hoard of taynix from Superiority control and escapes with them, with Doomslug, and with M-Bot, whose ship is destroyed and whose mind continues in a far smaller body. She hyperjumps home to Detritus carrying the secret of faster-than-light travel, which means humanity can finally move ships between stars; the orbital platforms are brought online and Detritus has a shield over it for the first time. The cost is that Winzik got most of what he wanted: he has proved the delver threat, gained sweeping authority, and holds both a war fleet and a means of pointing delvers at his enemies. Alanik has woken on Detritus and the impersonation has to be answered for, Jorgen has begun showing cytonic ability of his own, and the friends Spensa made at Starsight are scattered and know she is human.