Scarlet by Marissa Meyer -- 512 pages
Meanwhile Cinder escapes from her jail cell with another criminal, Thorne, who stole a spaceship. So, of course, they escape on this spaceship, but they can't stay in outer-space forever.
Emperor Kai is being hard pressed from all sides, but mostly from Lunar Queen Levana, who is furious about Cinder's escape, and threatening war if she isn't found.
Scarlet is the second book of The Lunar Chronicles.