Sometimes he has to poke around a bit to understand why a flag has been placed. A woman who might be a prostitute leans into a car window. Beneath a church marquee that says GOD LISTENS, someone has spray-painted TO SLAYER. Sometimes the software misinterprets a pattern of ivy for something obscene, or flags a kid walking to school for reasons Seymour cannot guess. He rejects or verifies the flag, draws an outline around the offending image with his cursor, and it’s gone, hidden behind a high-resolution bush or erased by a smear of counterfeit sidewalk.

The movement chime sounds; the other two men trundle off to lunch; Seymour stays put. By roll call, he has not moved for nine hours; the supervisor is gone; an old man sweeps beneath the teaching terminals; the windows are dark.

They pay him sixty-one cents an hour, which is eight more cents than the guys make in the furniture shop. He’s good at it. Pixel by pixel, boulevard by boulevard, city by city, he helps Ilium sanitize the planet. He effaces military sites, homeless encampments, queues outside medical clinics, labor strikes, demonstrators and dissidents, picketers and pickpockets. Sometimes he comes upon scenes that engulf him with emotion: a mother and son, bundled in parkas, holding hands beside an ambulance in Lithuania. A woman in a surgical mask kneeling on a Tokyo expressway in the middle of traffic. In Houston several hundred protesters hold banners in front of an oil refinery; he half expects to recognize Janet among them, twenty new frog patches sewn on her jean jacket. But all the faces are blurred, and he confirms the flag, and the software replaces the protesters with thirty digital sweetgum saplings.

Seymour Stuhlman’s stamina, the Ilium supervisors report, is remarkable. Most days he triples his quotas. By the time he is twenty-four, he is a legend in the Ilium Earth offices, the most efficient cleaner in the entire prison program. They send him an upgraded terminal, give him his own corner of the computer room, and raise his pay to seventy cents an hour. For a while, he manages to convince himself that he’s doing something good, removing toxicity and ugliness from the world, rinsing the earth of human iniquity and replacing it with vegetation.

But as the months tick past, especially after dark, in the isolation of his cell, he sees the old man in the dark of the library, wobbling in his penguin tie, holding the green backpack to his chest, and doubts worm their way in.

He’s twenty-six when Ilium develops its first treadmill prototype. Now rather than sit at a terminal and twitch through spaces with a scroll wheel, he’s walking through them on his own two feet, helping the AI cleanse the map of the ugly and the inconvenient. He averages fifteen miles a day.