Hemingway does not tell us Harry's last name; we know only that he is a writer and that he and his wife, Helen, are on a safari in East Africa. Their truck has malfunctioned, and, while trying to fix it, Harry scratched himself and neglected applying iodine to the scratch. Now, gangrene has begun to eat away at the flesh on his right leg. The stench is overpowering. However, he's not in pain — physical pain. All of his pain seems to be emotional pain of the seemingly sure knowledge that he is dying — and, worse than dying, he's dying without having written many stories that he'd planned to write.
Why didn't he write these stories? Harry believes that it was probably because he married a woman with a fortune. Her money poisoned his writing future, just as surely as gangrene is now poisoning his body and gnawing away at the few days of life that he has left.
When Harry is not being sarcastically savage to Helen, he drifts in and out of interior monologue flashbacks, remembering and recalling people and geography and incidents that he's kept in his scrapbook of memories. They will die with him. No one will ever write about them now.