Sue Trinder is a "fingersmith"—a pickpocket—living in the London slums. Orphaned as an infant, she was raised by Mrs. Sucksby, who trained her to be a thief. When Richard "Gentleman" Rivers comes to them with an elaborate scheme to swindle the rich Maud Lilly of her inheritance, Sue agrees to befriend Maud by becoming her maid. But as Sue and Maud grow closer, Sue begins to doubt her commitment to the scam.

After conspiring to leave Briar Court and marrying Rivers, Maud reveals that she has been in on the scam from the beginning. Desperate to be free from the prison of her uncle's house, Maud agrees to Rivers's plan to betray Sue, not expecting her feelings for the young woman to go beyond friendship. Then, a shocking truth comes to light that turns her world upside down.

As more of Mrs. Sucksby's plot is revealed, Maud escapes to the streets of London, naïve to the dangers lurking around every corner. With nowhere else to go, she seeks the help of one of her uncle's old business associates. At the asylum, Sue is subjected to cruel and inhumane treatments, but she has a trick up her sleeve to gain her freedom and take her revenge.