Why did they do it? Peter wondered—as he had wondered through all the nights he’d stood. Why did they come home, the ones who’d been taken up? What force drove the mysterious impulse to return? A last, melancholy memory of the person they’d once been? Did they come home to say goodbye? A viral, it was said, was a being without a soul. When Peter had turned eight and been released from the Sanctuary, it was Teacher, whose job this was, who had explained all of this to him. In its blood was a tiny creature, called a virus, that stole the soul away. The virus entered through a bite, typically to the neck but not always, and once it was inside a person, the soul was gone, leaving the body behind to walk the earth forever; the person they had been was no more. These were the facts of the world, the one truth from which all other truths descended; Peter might just as well have been wondering what made the rain fall; and yet, standing on the catwalk in the sharpening dusk—the seventh and final night of the Mercy, after which his brother would be declared dead, his name etched into the Stone, his belongings carted off to the Storehouse to be patched and repaired and redistributed at Share—he thought it. Why would a viral come home if it had no soul?