Fridays With Agent Kristin: What Is A Plot Catalyst?

So this may not be interesting to anybody else out there except book geeks (specifically writer book geeks). But as I have been working on query letters for the past two months, this advice was well-timed.

Basically, there needs to be something that happens in the first 20-30 pages of your book that gets the ball rolling (or in this case, gets the plot rolling). This event, is the axis around which everything else revolves. i.e. If this event never happened, there wouldn't be a book.

So in your most recent read, what was the plot catalyst?