What is the exposition of rumble fish

The novel opens five or six years after the main action, as Rusty James runs into his old friend Steve, whom he hasn't seen in all that time. They are on the beach, far from the original action. Rusty James has been "bumming around," not working since getting out of the reformatory after serving five years, and Steve is on vacation from college, where he's studying to become a high school teacher. Steve invites Rusty James to dinner, an invitation he has no intention of accepting. Steve is too much of a reminder of some bad times.