The Last Rapier by Dave Bullock

Air Force pilot Captain Jesse Hardin is thrilled when she’s offered the opportunity to test fly the top-secret prototype X-66 Rapier, the most advanced jet the world has never seen. However, her enthusiasm is soon tempered when she learns that a previous Rapier prototype, along with its two test pilots, vanished somewhere over the Pacific only a week before, and she’ll be flying the only other Rapier built. As Jesse begins flying the Rapier, she discovers that her backseat pilot is an imposter who plans to steal the airplane. Not knowing who to trust, Jesse decides the only way to protect the Rapier is to steal it herself…