Location: South Carolina
Rigaud is a mysterious character in general. He deliberately speaks obliquely about any specific knowledge or clout he believes he has with a character, and Dickens keeps him a riddle until the end of the book (this post is based on the novel, not on the film version).
From our initial meeting with Rigaud in the Marseilles prison of chapter one, we learn that he is a sinister figure, accused of having murdered his wife, but not convicted; his relationships with other characters in the story always center around furtive acts in which he is paid to do somewhat unscrupulous tasks such as spy on others or in which he "befriends" a character in order to gain some advantage over him/her. As soon as he has his advantage, he bides his time and then presses his advantage, always for money. Nonetheless, he seems to enjoy his position of power even more than the money he is able to extort out of his victims.
Rigaud acts in many ways as a foil to William Dorrit; both men see themselves as gentlemen who are in no way diminished by their status as inmates; both impose on others to gain favors without seeming to admit that they do impose; however, Dorrit, though self-centered, does not consciously aim to harm others; Rigaud personifies evil motives and takes perverse pleasure in every opportunity of watching others suffer.
The young black woman is a domestic maid and companion to "Pet," the much-loved and somewhat spoinled daughter of Mr. and Mrs. Meagles. Tattycoram (Harriet), is known by this nickname given by her employer. In Dickens's original version, she would not have been black, but the director apparently found the disadvantaged status of this girl similar to the social disadvantages often experienced by minorities.
We don't learn much of Tattycoram's background, but we can assume that she was an orphan or a girl whose family lacked the means to provide for her and who was sent to earn her living. Her placement with the affectionate Meagles family has obviously made her naturally resentful temper even more so as she compared her own situation with that of the much-loved daughter of her employers. Though Tattycoram is cared for and well treated by the family, she never feels that she has a home with them, and Mr. Meagles's habit of making her count to twenty-five whenever she begins to lose her temper irritates her more with each occurrence.
When the family meets Miss Wade, a fellow traveler who keeps to herself, this independent young woman observes Tattycoram's growing resentment, befriends her, and lures her away from the Meagles family by showing how well she understands the girl's feelings toward Pet, who in her eyes does not deserve her status of being universally loved.
Later, when Clennam tracks down Miss Wade in his attempt to clear his mother from presumed guilt in Rigaud's disappearance, Tattycoram recognizes that Miss Wade has just been projecting her own similar feelings of inadequacy and resentment on her maid, and that the stated design of "saving" Harriet/Tattycoram from her oppressive family has in fact deprived her of the only home she has ever known. Tattycoram has the strength to break with Miss Wade, who has become more a captor than a savior, and return to the Meagles family.