Possibly Sci-Fi, opening scene two jet fighters on routine aerial exercise suddenly interrupted by unidentified flying object zooming past them.

[SM]

I only remember reading the first chapter scene where two US jet fighters are conducting routine aerial exercise when suddenly an unidentified flying object flew very closely past them, taking them by surprise.

It's a long shot, I know... but it was a pretty well written first chapter and I wish I knew what the title of the book is so I can read it!