Sixpenny Girl by Meg Hutchinson
Helpless, Saran Chandler stands by as her mother and younger sister are sold by the vile Enoch Jacobs and herself narrowly escapes the same fate. When Enoch drowns, Saran swears that she will not rest until she has secured her family's release, but - penniless and friendless - barely knows where to start.
Saran's courage and virtue bring their own rewards: when she benefits from an act of kindness, she uses the gift to become a nailmaster in Wednesbury, a dark and grimy place, in thrall to the vicious Zadok Minch, whose godfearing exterior masks perverse tastes. Zadok Minch, the man who had once bought Saran's mother and sister to satisfy his evil lusts . . .