The actual novel doesn't have a solid plan, yet I'm already planning sequels/prequels lol
so i think the use of the prequel is pretty obvious: it'd be alice/isaac trying to survive ACE! except this time, we get to meet chloe, dean, among the actual 9 graduates. i guess throughout the story alice/isaac try to learn more about the suspicious disappearances of the other students (or i guess, they get hired by the govt so they don't need to complete ACE?) and investigate. i might make it kind of like the testing where something happens and they're forced to forget everything sus that happened at ACE.