Mori and her friends Julia, Benji, and Theo have never seen life beyond the walls of their perfect society, Old Harmonie. That changes when their new friend Ilana is threatened by the rules that are supposed to keep them all safe. They escape together, hoping to find help in Boston with Dr. Agatha Varden, one of Old Harmonie's pioneering founders.

But the outside world is nothing like they anticipated. As they face challenges they never expected and encounter a group of kids from the outside, Mori and the others begin to understand the complicated reality of their supposedly perfect community. With the help of these new friends, they just might be able to save Ilana . . . but at what cost?
This thought-provoking sequel to Megan Frazer Blakemore's stunningly imaginative novel, The Firefly Code, gives readers a chance to see our world in a brand new light.