Muriel Glass waits in her Florida hotel room for the operator to put her call through to her mother. The hotel is full for a sales convention, so she must wait a long time. She fixes her clothing, paints her nails, and reads a magazine. When the call does go through, Muriel reassures her anxious mother about her safety. Her mother is concerned about the erratic, reckless behavior of Seymour, Muriel’s husband. She hints at a car accident that Seymour and Muriel were involved in and suggests that Seymour deliberately crashed Muriel’s father’s car into a tree. She reminds Muriel of the strange and rude things Seymour has said to members of Muriel’s family. Seymour has recently returned from the war, and Muriel’s mother believes that he was discharged from the military hospital prematurely. Muriel is not as concerned as her mother. She is preoccupied by the fashion at the resort and the evening’s events. In the evenings, there are formal dinners and cocktail parties, at which Seymour often sits apart, playing the piano. The resort is full of society people, although Muriel feels that the quality of these people has diminished since the war. She tells her mother that Seymour is on the beach by himself.
On the beach, three-year-old Sybil Carpenter lets her mother put sunscreen on her body. Mrs. Carpenter then sends Sybil away so that she can go have cocktails. Sybil wanders far from the part of the beach where the hotel guests are situated. Eventually, she finds Seymour, who knows her. He tells her he likes her blue bathing suit, but her suit is yellow. Sybil accuses him of letting another little girl, Sharon Lipschutz, sit on the bench with him while he played the piano. Seymour assures Sybil that she is his favorite. Sybil tells Seymour he should push Sharon off the piano bench next time. As they get ready to go into the ocean, Seymour tells Sybil they should look for bananafish. They then discuss the tigers in one of Sybil’s children’s books, Black Sambo, as well as Sybil’s fondness for olives and wax. Sybil asks Seymour whether he likes Sharon Lipschutz, and Seymour tells her that he does, especially the fact that she is nice to small dogs and always kind.
In the water, Seymour puts Sybil onto the raft and says it’s a perfect day for bananafish. He explains that these are normal-looking fish that swim into banana holes and greedily eat all the bananas inside. As a result, the bananafish become so fat that they cannot leave their holes and die. Doubtful of the fish at first, Sybil tells Seymour that she sees a bananafish with six bananas in his mouth. Seymour kisses the arch of Sybil’s foot. Sybil protests, and when they get out of the water, Sybil runs back to the hotel.
Seymour, alone again, collects his things and returns to the resort. On his way to his room, he accuses a woman in the elevator of looking at his feet. When the woman denies it, Seymour becomes irate, calling her a “God-damned sneak.” The woman leaves the elevator. Seymour proceeds to his room, where Muriel is napping. Sitting on the other bed, he watches her. Then he takes a gun from his luggage and shoots himself in the head.