S . . . is for a lot of things (PG-13)
"Prologue" is just a fancy word for the stuff that happened before the story (I made that up just now *snork*) Just read the darn thing.
When Max's sister Marcy finds the body of a Control Agent, he rushes to her side --only to run away from his duty to Control and into the path of Kaos.
99 is sent to infiltrate a Kaotic girls school just as Max and Marcy learn that teaching could be hazardous to a spy's health.
Max's persona with Control begins to really fall apart when he sneaks a peek in the morgue and gets caught by a certain Chief of Control. He is subsequently confronted by 99, which also fails to score him points. These social issues, of course, leave Agent 86 distracted, thus causing someone close to him to fall into Kaos.
Marcy discovers that being gassed can be an itchy situation while the Chief makes a critical decision regarding what to do about their strange and confusing case. Max entertains the idea of getting a little closer to 99.
Max awakes from his slumber to find 99 and Marcy missing. As he attempts to rescue them, he finds himself snared in a Kaos trap.
And epilogue is a fancy word for the stuff that happened after the story. I made that up too.