In the short story "Dusk," the bar of soap belongs to the old man who sat down next to Gortsby first.
The old man sat down on the park bench next to Gortsby. His bar of soap must have fallen from his coat.
The young man sits down after the old man hast left. The young man tells a story about buying a bar of soap. He tells about losing his way back to his hotel. Gortsby tells him the story would be credible if he could produce a bar of soap. With this comment, the young man leaves.
Then, Gortsby finds a bar of soap under the park bench and thinks it belongs to the young man. Gortsby chases the young man and gives him the bar of soap. Gortsby also gives the young man a loan of money. Since the bar of soap proves the young man's story, Gortsby believes the young man and loans him money for the night.
Passing the park bench where Gortsby had been sitting, he sees the old man looking for something. Gortsby inquires. He asks the old man what he is looking for. The old man says a bar of soap:
As Gortsby walks back, he passes the bench where he had been sitting. He notices the old man who had also been sitting there earlier. The old man is now searching for something. When Gortsby asks if the old man has lost anything, the man replies, “Yes, sir, a cake of soap.”
Gortsby feels like a fool for trusting the young man. He has loaned money that he will never see again.