Bundled all together, these villains have nothing on Mumtaz.
The owner of Happiness House is almost the quintessential villain: greedy, cruel, manipulative, and violent. There's little complexity to her character. She rules through fear, lies, and violence, and her tactics are incredibly effective.
Little motivates Mumtaz except for greed, and almost all of the actions she takes are to maximize her profit margin. She clearly has a train of employees extending to Nepal for the express purpose of giving the girls in the brothel no option of escape. As she says to Lakshmi:
"Do you know the way home? […] Do you have money for the train? Do you speak the language here? Do you even have any idea where you are?" (70.Sold.11)
And when Lakshmi tries to run from her first rape, Mumtaz shaves her head and threatens to slice Lakshmi's throat if she doesn't comply. The threat is real enough that Shahanna, who is in the room, opens her eyes "wide with fear" (70.Sold.27). When Lakshmi still refuses to work for Mumtaz, the owner of the brothel beats and starves her to within an inch of her life.
One of Lakshmi's flaws is that she believes that justice will prevail. Mumtaz quickly turns that belief on its ear with her behavior and constant lies. Instead of telling Lakshmi she was bought for ten thousand rupees (which she was), Mumtaz tells her that she paid twenty thousand rupees (90.Changes).
Even when Lakshmi has an STI (sexually transmitted infection), Mumtaz only gives her medicine because it's more cost-effective to help Lakshmi than it is to find a new worker. And despite the fact that for a moment Lakshmi loves her "like a mother, for giving me the medicine […] for not throwing me out on the street, for caring for me" (128.TheCostofaCure.21), Mumtaz doesn't appear to care. In fact, her response is what we've come to expect from her:
"You'll be able to work off the cost of the medicine in a few days." (128.TheCostofaCure.25)
Always concerned with the bottom line, Mumtaz is.
Mumtaz doesn't rule alone, though. She hires goondas, men who carry out beatings she orders, and she pays off a policeman each week so that she can continue running her business (106.Police). Inside the house, she has Shilpa spy on the other girls. In fact, Mumtaz rarely interacts with the girls in the brothel.
Her power is such that the climax of the last chapter, when Mumtaz cannot prevent Lakshmi from leaving the brothel, is actually somewhat anticlimactic. It's not surprising that Mumtaz easily lies and tells the Americans and good police officers that there are no young girls in the house. And we're not shocked when she spits her disgust at Lakshmi. Perhaps—and we'd certainly like to think—Mumtaz's great weakness is her belief in her own infallibility, that she will continue to escape justice and the law, that no girl would dream of acting on a desire to escape. Because if this is true, then eventually Mumtaz will be stopped.
As it stands though, the ending for Mumtaz does not satisfy our own desire for justice. Do you think Happiness House will eventually be shut down?