The Persephone Protocol

Everyone at Stenfod thinks Chloe Mitchell got in only through her boyfriend, a dead weight who cannot tell a neural interface from a port. Tyler humiliates her in public; Rachel whispers insults. No one knows she is "G", the hacker who blacked out the global mecha network for six hours, her S+ file sealed by her late grandfather.

When Stenfod faces MAT live, Chloe lifts the seal, awakens Hide-and-Seek, and pilots her mecha Persephone to win in one minute forty-seven seconds. G is back.