"A Perfect Day for Bananafish" takes place at a resort hotel in Florida in 1948. The first scene features Muriel Glass, a young woman who has been married for five years to Seymour Glass. Muriel is on the phone with her mother, discussing Seymour. It seems that, since getting back from the war (WWII), Seymour just hasn't been the same. He's mentally unstable, and seemingly incapable of functioning normally in a social environment. Muriel's mother is scared for her daughter and wants her to come home. But Muriel doesn't seem to be taking the issue very seriously at all. She insists that Seymour is fine.
The second scene takes place on the beach outside the hotel, where a little girl named Sybil Carpenter waits while her mother puts sun block on her back. "See more glass," the girl keeps repeating, though her mother has no idea what that means. Finally Mrs. Carpenter lets the little girl run off to play. Sybil runs to a deserted part of the beach to find Seymour, with whom she's apparently struck up a friendship during her stay at the hotel. Seymour is obviously wonderful with children; he jokes around with Sybil, and she's clearly enamored with him.
The two of them head into the ocean together, and Seymour explains to Sybil all about bananafish. They're normal little fish, he says, until they swim into a banana hole and gorge themselves on bananas. Then they're too fat to get back out again and they die. Sybil, playing along, exclaims that she's seen a bananafish with six bananas in its mouth. Seymour then kisses her foot and says it's time to go back.
Once they've parted ways, Seymour plods along back to the hotel. In the elevator, he accuses an adult woman of looking at his feet. She thinks he's crazy. Seymour makes it to his hotel room, where Muriel is asleep on one of the twin beds. He takes a gun from his suitcase, sits on the other bed, and fires a bullet through his temple.