Reactor: Those Beyond the Wall, Micaiah Johnson’s second novel, can be read as a standalone, or you can read it as a followup that’s something of a mirror image to The Space Between Worlds, her 2020 debut. Space was set mostly inside the walls of Wiley City, where an unlikely survivor named Cara found an unusual way to make a life among the privileged. Beyond is set in the nearby desert community of Ashtown, under the sometimes-deadly glare of the sun. That sun is far from the only deadly thing in Ashtown.
Both places are changed by a technological innovation that allows people to move between worlds. Each person exists, or existed, in every world, though their lives are different—sometimes more different, sometimes less. There are catches, because there are always catches. It’s not an easy experience, seeing the other yous that might have been.
This book isn’t about technology, though. (Johnson is very aware of the fine line between magic and science.) It’s about revolution, and it’s about Mr. Scales, one of the many runners who serve Nik Nik, the emperor of Ashtown. Technically, Scales is a mechanic, but like her fellows, she’s also a killer. She has been other things, and lived other lives, but at this moment, in this life, everything goes to hell when she watches a friend die horribly. There is no killer. Helene X just folds in on herself, bones breaking and reversing, as Scales tries to hold her together.
The threat that causes these terrible deaths—because of course there are more—affects primarily people in Wiley, but trouble in Wiley quickly becomes trouble for Ashtown. In the city, a scientist named Adam Bosch understands better than most what is happening. When Scales and her colleagues bring him to their emperor, a whole host of events are set in motion.
The question of who is killing the mangled dead is less of an issue than the matter of how to stop it. This is the catalyst for Johnson’s story, but its engine, its heart, is Scales, who gradually turns her attention to the pre-existing, systemic issues that affect everyone in Ashtown. The people of this world need to put a wall between themselves and the entitled, brazen enemy that would destroy them. But there is an existing wall that isn’t doing Ashtowners any good.