Many of today's novels, television shows, and movies have plots based on the classic Greek tragedy. Mystic River, a film directed by Clint Eastwood, follows this formula in some respect but it would be note worthy to examine how it differs.
Dave Boyle, Jimmy Markum, and Sean Devine are playing in the street when a sedan pulls up and then drives away with Dave in the back. The guys in the car were pedophiles who scarred Dave for life. This incident, considered to be the mysterious past sin of the Greek tragedy, influenced the three boys profoundly. As a result they would grow up to be different types of men.
Despite the kidnapping, Dave seems to lead a normal life. With a wife, a son and a home in suburbia Boston. Jimmy becomes the boss of a small criminal organization and can be interpreted as the king in his role as a community leader.
Sean on the other hand grows up to be a police detective. He can be seen as the hero with his position in law enforcement. The tree guys know each other but don't remain close.
The murder of Jimmy's daughter Katie brings the three men back into each other's lives. On the same night Katie was killed Dave kills a man he thought was molesting a kid. With the mysterious evidence surrounding Dave's homicidal incident, Jimmy is led to mistakenly believe (his hamartia) that Dave is responsible for the death of his daughter. He is thus compelled to deal out 'justice' upon his childhood friend and executes Dave in the exact manner that Jimmy killed a fellow criminal (Harris) when they were young men.
It turns out that Harris' younger son, Silent Ray, is Katie's murderer and not Dave. Silent Ray killed Katie...