Ok, my dad used to tell us about a book and I would love to find it for him (and for me!) I *think* it was about a suicidal fighter pilot who was recruited by aliens to help them defend themselves from another warring race. He quickly becomes their top fighter. He is somehow wounded and captured, and his life is saved by another prisoner, a woman who is a doctor and maybe a princess or of some other highborn standing. They escape and help defeat their captors. He returns to Earth with her. He has been paid in diamonds and his space ship, which he keeps hidden by submerging it in a lake. If anyone could help point me in the right direction, I would really appreciate it! Thank you.