Great question! Well, none of my secondary characters have actually hi-jacked any story, though some have started talking in my head so loudly that they had to have their own book written next! That's how my series' get written.
But in Recipe For Love, there is a chapter that my editor wanted me to leave out because it doesn't have anything to do with the main romance between Patti and J. T., her tattooed Romani biker. This chapter is about an encounter in a car and involves Juanita and Edgar, friends to Patti and Tegan, the heroine from the first book in the series. After going to the hospital to see Tegan's new baby, fathered by Edgar's brother Alejandro, Juanita and Edgar have a passionate encounter in their car because seeing a new baby gets them both hot and bothered. They already have 7 kids, but Edgar very persuasively convinces Juanita they need to have uno mas.
I told my editor that chapter had to stay in because Juanita and Edgar were never going to have their love story told by me, but their kids were going to be the stars of the rest of my Reyes Romance novels. They were both okay with that, as long as I "let" them have one chapter to show my readers how passionate even a long-term marriage could be. Crazy, huh? But that's how things are in the mind of an author. The characters make deals with me, and I write their stories so they can grow by living in the minds of readers. As my slogan in my bio goes, "My kind is a very crowded place, but I like it like that."
For the next author's take on this fun question, please go to:
A.J. Maguire http://ajmaguire.wordpress.com/