In this short story, we meet Nevil Clavain, one of the protagonists of the Revelation Space cycle, Galiana, the founder of the Conjoiner faction, and Sandra Voi, an important person in the Demarchist faction.
The story begins on Deimos, where Nevil Clavain, a high-ranking officer in the Coalition for Neural Purity is preparing to go down to the surface of Mars. His brother, Warren, is pushing for war with the Conjoiners. Eventually, Clavain and Voi depart and fly down towards the Great Wall of Mars, which turns out to be a massive construction that completely envelops part of the planet's surface (enough to cover a city) and the atmosphere above it. As they descend, they are attacked by robotic "worms"- war machines from the previous war with the Conjoiners. Clavain destroys the first worm, but more arrive and kill Voi. Clavain just succeeds in reaching the Conjoiner base. Galiana shows him around and he suggests that the Conjoiners and Coalition team up to attack Phobos, which is apparently infested by the worms. It is revealed that the Conjoiners are constantly deploying shuttles that try to escape the planet, but are always shot down by Coalition satellites. Clavain also meets Felka, a girl who was part of an experiment to further improve human intelligence by altering the brain in the womb. It failed miserably and Felka seems completely uninterested in anything except the mysterious game she is playing – she keeps waving her hands around in a pattern.
While negotiations are under way, Clavain's brother Warren attacks the Conjoiner base. Clavain is knocked out in the ensuing battle, but the Conjoiners are able to hold off the first three waves. By then, however, their defences are exhausted and they will not last another attack. During surgery, Clavain receives basic Conjoiner implants, enabling him to see the complicated readouts that surround every Conjoiner and their devices. With these, he can see that Felka is not simply playing a game: she is actually controlling the Great Wall's repair mechanisms. However, the attack has damaged it so badly even she cannot keep it intact for long and soon the wall will collapse, causing the atmospheric pressure inside to be released and tear the base apart. Clavain is confident that the Conjoiners will soon be wiped out.
Galiana reveals the Conjoiners' plans to escape: the shuttles they were sending up were no more than distractions – they were filled with brain-dead clones before they took off. The Conjoiners had really been digging a tunnel that they use to launch spaceships to Phobos, which they have hollowed out and turned into a massive shipyard. The Coalition was unaware the Conjoiners had control of the moon. As Galiana prepares to leave, Clavain first runs back and takes Felka with him, unable to leave without her. They take off and head for Phobos. Galiana warns Clavain that the deceleration upon landing will kill him unless he receives more extensive neural implants. He accepts, knowing he is about to defect from the Coalition.