Perfect Ruin by Lauren Destefano
Goodreads Summary: On Internment, the floating island in the clouds where 16-year-old Morgan Stockhour lives, getting too close to the edge can lead to madness. Even though Morgan’s older brother, Lex, was a Jumper, Morgan vows never to end up like him. She tries her best not to mind that her life is orderly and boring, and if she ever wonders about the ground, and why it is forbidden, she takes solace in best friend Pen and her betrothed, Basil. Then a murder, the first in a generation, rocks the city. With whispers swirling and fear on the wind, Morgan can no longer stop herself from investigating, especially when she meets Judas. He is the boy being blamed for the murder — betrothed to the victim — but Morgan is convinced of his innocence. Secrets lay at the heart of Internment, but nothing can prepare Morgan for what she will find — or who she will lose.