One day when the boys are eleven and hanging out in front of Sean's house, a car pulls up and two men identify themselves as cops, but they aren't, and they take Dave away in their car. This is the first, large event in the novel. Towards the end of the novel, Sean wonders what if he or Jimmy had gotten into that car. Lehane puts the reader on notice that this is a novel about how lives are twisted, how lives are horribly ruined by twists of fate. You will not come away from this book feeling good about humanity.
Mystic River is character-driven, but intentionally so.
There isn't a short-changing on plot development and execution here, merely that the plot is second string in this orchestra. I would be hard placed to think of a more intensely and compellingly drawn character than Jimmy Marcus. Jimmy is a gorgeous mosaic of a man who not only is feeling an ultimate grief, the loss of a child, but he is morally conflicted. He is the heartbeat of Mystic River. Jimmy Marcus grows up from the little boy hanging out with Sean and Dave into a criminal.