The purpose of a sub-plot is to add depth to a story that may otherwise be one-dimensional in terms of what actually happens. In Ruined, there is drama and despair but the story, although desperately sad and all too real, is fairly typical and one that cannot have a happy ending in terms of the plight of these women in the war-torn Democratic Republic of Congo - or any similar country. Therefore, Lynn Nottage adds sub-plots to ensure that the viewer becomes part of the daily lives of individuals rather than a mere spectator of a larger story that they are all too aware of but feel far removed from.
The very fact that Mama Nadi is running a business and must consider what is best for business is a sub-plot that ensures that the story maintains its ability to discuss real life. In discussing Salima, Mama reminds Christian that she has "a dozen girls like her" and so, wonders why she should pay for another. This is the harsh reality. In discussing the "ruined" Sophie, Mama is angry that she now has another burden and she wonders about the usefulness of these girls. Mama also questions Christian's hypocrisy as he watches her do her best which constantly involves compromise. This links to the main plot and intention of the play in revealing the atrocities and their part in the every day lives of so many affected people. In order for Mama to actually help these girls, she has to remain business-like, almost a contradiction.
Mama Nadi discusses business with Mr Harari who is barefoot and Mama is curious as it makes little sense. He is unimpressed that he is constantly "liberated" of his shoes by mere children who think that they are "rebel" soldiers and he aware how disempowering and ridiculous his situation seems. He is a diamond merchant but cannot even keep his shoes when he comes to do business here. This ties in to the larger issues and how much people take for granted. No one would expect a foreign diamond merchant to have any difficulties. He represents prosperity and even freedom as he can leave at any time and yet, he is unable to improve the situation for these girls. Mr Harari knows how it is to be friends with everybody and nobody at the same time, always cautious. This makes the viewer realize how complex the girls' circumstances are. Even the girls themselves bicker over small things, things that are important to them - such as the fact that Sophie is "ruined" - and, according to Josephine, this makes her more unfortunate than her; a fact that seems absurd to an outsider.
Sophie likes to read romance-type novels and Mama feels this gives her an unrealistic impression of reality. This is minor but contributes to the story because this reveals that Sophie and the other girls, for all their misfortune, have the same aspirations as any other young girl may have, regardless of her circumstances. They want to be loved and to be safe, things that they should be able to take for granted. This intensifies their desperate position and the injustice. The fact that Mama is, herself, "ruined" completes the desperate picture but also adds a glimmer of hope for others; if there is some hope for her then maybe there is something more for the girls.