The Sword of Io by M. L. Buchman

Captain Christine Merrill ranks as the toughest and best pilot in the Army’s Night Stalker fighter regiment. She also hides one of the darkest secrets in the solar system.

Sergeant Phil Parello keeps a secret of his own beyond his growing attraction to Captain Christine the Fighting Machine.

Crashed on Io’s lethal surface, the only way to survive is together. They must share their hearts and their secrets to survive The Sword of Io.