The title of Saki's short story,"Dusk," is appropriate given the setting of the story. Norman Gortsby, the protagonist of the story, defines dusk as "the hour of the defeated." Given that Norman is out at dusk, one can only asume that he will find defeat by the end of the tale.
For Norman, dusk provides the cover that those who are hiding their "shabby clothes and bowed shoulders and unhappy eyes." Not wanting to be seen by the successful, dusk provides the shadowing needed to hide their failures.
At the end of the story, Norman has fallen victim to one of the successful. Spinning a story about having no cash and friends, a young man is able to prove Norman to be one of the people of dusk. Therefore, the title of the story is appropriate given not only does it describe part of the setting, it describes the figurative partial darkness of Norman's trust in mankind.