Rabbit is Rich picks up the story begun in Updike's Rabbit Run (1961) and continued in Rabbit Redux (1971), of Harry Angstrom, Rabbit, in his mid-forties in the late 1970's. He is the Sales Manager and part owner of Springer Motors Toyota, in the fictional town of Brewer, PA. Harry is at the lot when two young people come in looking for a car. Harry takes them for a test drive and gets the notion that the girl may be his daughter. After the young people have left Harry talks about them with Charlie Stavros, his colleague at Springer Motors, but Charlie has paperwork he is trying to complete, so Harry leaves for the drive home. On his trip home, we are given a tour of several parts of Brewer, PA.

At home, there is great tension because Nelson has written that he is coming home and bringing Melanie. Nobody knows who Melanie is. Bessie is especially upset, but Janice and Harry get her calmed down. A few days later, they are at the pool at their country club and we get to meet their country club buddies. They get a message to call Bessie. It turns out that Nelson and Melanie have arrived. Driving home from the club, Harry tells Janice about the girl he thinks may be his daughter and immediately realizes it was not a good idea. He dreads seeing Nelson; he remembers when his home burned down, a young girl named Jill, whom Nelson had loved like a sister, had died. Nelson has not forgiven him.

Melanie gets a job as a waitress, and Harry takes Charlie over to the restaurant to meet her. They hit it off. The Angstroms invite Charlie to come to dinner where he has another chance to see Melanie. Nelson is out for the evening with Billy Fosnacht (and with Harry's Corona). When he comes back, it seems there has been a small accident and the Toyota has been scraped on the side.

Harry drives down to the farm country around Galilee and locates the farm where Ruth Byer, with whom he had an affair about 20 years ago, lives. She is the mother of the girl who appeared with Jamie Nunemacher in the showroom. He imagines a conversation with Ruth, but gets scared and runs away.

Harry, Janice and Bessie are away in the Poconos. As soon as they get home, Nelson wants to take Harry over to the lot. He has something he wants to show him. It turns out to be three convertibles that Nelson has bought—or has caused the dealership to buy. Harry is extremely critical of the idea and gets on Nelson to the point that Nelson gets into one of the convertibles and rams it into one of the others.

A couple of days later, Harry is at the club. Janice calls to tell him to come home immediately. It turns out that Pru—introduced as Nelson's fiancé, is there and she is pregnant. Planning for a wedding begins immediately. Before the wedding, Harry talks with Nelson about the situation and indicates that if Nelson wants to get out of the whole thing that he will help him do it. Nelson says he is okay with marrying Pru.

Harry buys a few thousand dollars of gold Krugerrands. That night when he shows them to Janice, they end up making love with the coins dripping over their bodies. The wedding goes off as planned. At a party with their country club friends, Harry suggests that the six of them should plan to take a Caribbean vacation together in January. They agree with some excitement. Harry takes another drive down to Galilee. This time he knows exactly where to go, but again he gets scared. While he is hiding in a line of trees, a big dog comes barking at him. Harry works his way back to his car and turns tail.

Nelson and Pru are at a party at Slim's. Pru is dancing, but Nelson is just sitting down and having a few beers. He falls into conversation with Annabelle, who is there with Jamie Nunemacher. They have moved up to Brewer from Galilee and are living together. As they are leaving the party, Pru falls on the stairs and breaks an arm. She winds up in the hospital where everyone is very worried about the baby, but the baby is fine. Pru gives birth to a little girl not long after the accident. Everyone is delighted.

Harry sells the gold Krugerrands and buys a bunch of silver coins. He has made a nice profit on the gold. They have a meeting with Bessie Springer and tell her that they have been looking at houses.

The day eventually comes when they go to the Caribbean with their friends. They swim, play golf, go sunfish sailing and generally have a wonderful time. At dinner someone suggests they swap wives night-by-night. They have a serious discussion about the idea and work out a set of ground rules to agree on. Harry is picked by Thelma, much to his disappointment. He is really hot for Cindy Murkett, but that will have to be another night. Thelma actually is very fond of Harry—something he had been totally unaware of. She gives him a night of ardent love. The next morning they are awakened by people pounding at the door of their cabana. It seems that Harry and Janice have to return home immediately; Nelson has run off.

Bessie had the good sense to get Charlie, who had been let go to make room for Nelson at the dealership, to come back, so they are still selling cars. Harry makes another expedition down to Galilee and this time gets up enough nerve to actually knock on the door and have an extensive conversation with Ruth. She swears to him that her daughter Annabelle is not his child. They get a postcard from Nelson. He is back at Kent State enrolling for the new semester.

Rabbit and Janice are in their new home. It is Super Bowl Sunday. Bessie and Pru have come over to see the new place and watch the game. While Janice is showing Bessie the upstairs, Pru finds Harry sitting in a wing chair in his den. She puts the new baby, his granddaughter, into his lap.