Jim Thompson, a very good writer of hardboiled novels, describes what he calls "short cons" in his novel The Grifters, which has been made into a movie like many of Thompson's other novels, including The Getaway. Both Saki's story "Dusk" and Roald Dahl's story "The Umbrella Man" are about the so-called short con. The con men are only after small sums of money. Actually in both cases the amount in question is one pound. The umbrella man can only work his scam when it is raining, whereas the con man--or con men?--in "Dusk" can operate almost any evening except when it isn't raining.
It appears that both the young man and the elderly gentleman in "Dusk" are working the same scam, but this is something that is never made perfectly clear. It is barely possible that neither of the two men Gortsby encounters is dishonest. He would only know for sure that at least one of them was a con artist if the elderly gentleman started to tell him how he had come out of his hotel room just to buy a cake of soap and then had forgotten the name of his hotel and was in danger of having to spend the night outdoors.
With "The Umbrella Man" the reader is not left with any doubt about what the old man was up to. However, there seems to be one unanswered question. What would the young narrator's mother do with the unbrella? She has acquired a silk umbrella worth twenty pounds for one pound. She knows it is stolen but would have no way of knowing who it belonged to or which pub it had been stolen from. Will she keep it? What is her alternative? We suspect that the girl's mother will keep the valuable umbrella and try not to remember how she obtained it.
Saki's story "Dusk" leaves unanswered questions too. Which of the two strangers was the con man? Were they both con men? Were neither of them con men? It seems most likely that both men are working the same "short con" but that the elderly gentleman, having more experience, has done exactly what Gortsby tells himself the young man should have done.
"It was a pity," mused Gortsby, "the going out to get one's own soap was the one convincing touch in the whole story, and yet it was just that little detail that brought him to grief. If he had had the brilliant forethought to provide himself with a cake of soap, wrapped and sealed with all the solicitude of the chemist's counter, he would have been a genius in his particular line."
Con men in Jim Thomppson's novel always learn their trade from older tutors, some of whom are legendary. There is a possibility that the elderly gentleman, who was sitting beside Gortsby first, might have actually been the younger con man's mentor and had taught him the story about the lost hotel and the cake of soap. The elderly gentleman leaves with the intention of coming back to look for the soap he purposely dropped, and in the meantime the younger apprentice unwittingly selects the same victim to try the same story on.
Both stories depend upon the setting. In one story it has to be around dusk; in the other story it has to be raining. In "Dusk" it has to be dark but not too dark. The con men are violating the law, and the law in England in Saki's time was undoubtedly much more strictly enforced by policemen who patrolled on foot. Furthermore, if con men tried approaching strangers it the dead of night they would only frighten them away. Dusk was essential in Saki's story and rain was essential in Dahl's.