Dusk is used first to establish a mood. It is the time when the day ends and the night takes over. Daytime is busy. Nighttime is relaxed. No doubt the viewpoint character has put in a long day at work and is now savoring the enjoyment of doing absolutely nothing. He is obviously unmarried and lives in a small furnished apartment. He doesn't want to go home to his lonely rooms. He is not hungry. He is enjoying looking at people who are worse off than he is. At least he is young and has a steady job. He has money in his pockets. He can afford to give away a sovereign, a coin worth one pound.
Assuming that the young stranger who sits beside Gortsby and tells him a hard-luck story is a confidence trickster, he is breaking the law and he knows it. The London streets were patrolled on foot by uniformed policemen who were acquainted with most of the regular inhabitants and the shopkeepers and would naturally keep an eye on strangers. Dusk would tend to bring out all sorts of shady characters because their activities would be less conspicuous. However, many of them would have a narrow window of opportunity. By nightfall most of the respectable citizens, including Norman Gortsby, would be safe indoors. Only the really hard-core criminals such as armed robbers and burglars would be on the streets after dark.
The setting of "Dusk" is used to make the young stranger's story plausible. He is ostensibly in trouble because night will soon be falling and he only has a couple of pennies in his pocket. It will not only be very cold at this time of year--early in March in a cold northern climate--but it will be extremely dangerous to be out on the streets or trying to sleep on the embankment by the Thames. The young man can't even afford to sit in a pub, assuminig he could find one open all night.
The setting of dusk in a big city forces the reader to visualize all the characters in the story as shadowy and anonymous. There is no way of trying to read their faces. This contributes to the ambiguity of Saki's story. How did such a coincidence come about that the young man claimed to have lost his cake of soap and when Gortsby gets up to leave
. . . an exclamation of concern escaped him. Lying on the ground by the side of the bench was a small oval packet, wrapped and sealed with the solicitude of a chemist's counter. It could be nothing else but a cake of soap, and it had evidently fallen out of the youth's overcoat pocket when he flung himself down on the seat.
There seem to be several possibilities. The young man was telling the truth but had lost his cake of soap elsewhere, while the elderly gentleman who had been sitting there before had lost his soap by the bench. Or: the young man was not telling the truth but got a big surprise when Gortsby handed him a sovereign and a cake of soap. Or: both the young man and the elderly man were working the same "short con," to use Jim Thompson's expression in his novel The Grifters (see referece links below). But the elderly gentleman, being more experienced in working this particular grift, had left a cake of soap by the bench with the intention of coming back and using it as a gambit to start a conversation with Gortsby.
Dusk makes everybody a shadow. Saki's story is more effective because everything occurs in the gathering dark. Policemen are handicapped by not being able to see what is going on in this twilight world. Dusk brings out stealthy predators, just as it does in the animal kingdom in the jungle.
Throughout the story dusk has played an important role.Dusk symbolises halflight when things cannot be seen clearly or people do not want to be seen clearly especially the ones who are unsuccesful.Many times a clever man like Gortsby is proved wrong at dusk as he could not judge the young man and was outwitted by him.IT is the time of dusk when light is poor that con men comeout to cheat people which they darenot try during the day.Dusk is the main character of the story it is the right setting as the young man told his story during the day he could have gone for help easily,Dusk is appropriate time for the the story to take shape.dusk was the reason the soapcake was not seen by the youngman and the old gentleman to whom the cake belonged.