Every book really starts some time before the first chapter, and these are scenes usually deleted so the novel starts with a bang not a whimper.
Each novel in the Meeting the Enemy series had back stories--an encounter at a flight training academy, a mission from twenty years before, an interview with a security company whose decor brings back bad memories, and a grueling test for a new operative in the Directorate that creates a dilemma thirty years later.
See how it all got started.