In an example of dramatic irony, Robin fails to recognize that the scarlet-clad woman he meets while walking the streets of Boston is a sex worker, instead believing her half-hearted story that she is Major Molineux’s housekeeper (a story she tells to lure him inside her house). The irony comes across in the following passage, when Robin first calls to the woman:
All that Robin could discern was a strip of scarlet petticoat, and the occasional sparkle of an eye, as if the moonbeams were trembling on some bright thing.
“Pretty mistress,”—for I may call her so with a good conscience, thought the shrewd youth, since I know nothing to the contrary—"my sweet pretty mistress, will you be kind enough to tell me whereabouts I must seek the dwelling of my kinsman, Major Molineux?”
Hawthorne intentionally includes details in this passage so that his readers will realize what the young Robin does not—that this woman is a prostitute. First, by mentioning the woman’s “strip of scarlet petticoat” as well as the “occasional sparkle of an eye,” Hawthorne hints at her coquettish intentions. The color scarlet here signifies lust and sexuality (a color that Hawthorne uses in similar symbolic fashion in his novel The Scarlet Letter).
That Robin “know[s] nothing to the contrary” than to assume the woman is simply a “sweet pretty mistress” demonstrates his innocence and naivety. He has only just arrived in the city after spending his first 18 years in the country and fails to recognize that this woman cannot be trusted. It is only because a night watchman walks by and scares the woman back inside that Robin is spared from entering her house.
