Orphaned Teenage girl lives two lives on habitat 3091, one of hundreds of thousands of habitats that consistitute Dyson Sphere Alpha. One life is in accordance with Magnusson's rule. Magnusson has lead the human race for the last 10,000 years in the contruction of the dyson sphere, but it is almost completed now. 

The other life Emma Miner lives, is one where she harbors a rebellion fugative. He's her only hope of escaping the habitat and fleeing to the rebellion, or what remains of it. But when she is discovered and taken prisoner, she discovers something else. 

Someone else lives in her brain. And that someone else is a devil.