How did Nolan end up exiled to the 14th?

Exiled leads seamlessly into the novel Destroyer, detailing how Nolan first encountered agents of the Void Wraith.

The Void Wraith are not yet ready to begin their war against the Milky Way. Experiments must be conducted. DNA mapped. Slaves created. They move cautiously, their agents infiltrating the governments of every major race. But every invasion leaves clues - clues that one OFI officer has stumbled across.

Stations are disappearing. Whole populations gone seemingly overnight. Commander Nolan convinces the Office of Fleet Intelligence to dispatch him to investigate. He discovers something far more sinister and far reaching than he imagined. Along the way he'll sacrifice his career, his relationship, and his faith in the Unified Earth Fleet.