Who is the main subject in the poem, A Midnight Woman to the Bobby?

The poem's titular character, and the speaker who narrates its story, is a "midnight woman." This euphemism, though not apparently in common use at any point, would seem to refer to the more common term "lady of the night," meaning a prostitute. The use of "midnight" as a characterizing term also summons the image of darkness, implying the speaker's social role as a Black woman.