Question: What is the title of Erika Mitchell's novel that reached number 1 on the "USA Today" best seller list?
Related documents: [0]  [DOC] Erika Mitchell (born 7 March 1963), known by her pen name E. L. James, is an English author. She wrote the bestselling erotic romance trilogy "Fifty Shades of Grey", "Fifty Shades Darker", and "Fifty Shades Freed", along with the companion novel ""; and under "Snowqueen's Icedragon" the Twilight fan fiction "Master of the Universe" that was the basis for the Fifty Shades trilogy. [END] 
[1]  [DOC] Fifty Shades Darker is a 2012 erotic romance novel by British author E. L. James. It is the second instalment in the "Fifty Shades" trilogy that traces the deepening relationship between a college graduate, Anastasia Steele, and a young business magnate, Christian Grey. The first and third volumes, "Fifty Shades of Grey" and "Fifty Shades Freed", were published in 2011 and 2012. The novel is published by Vintage Books and reached No. 1 on the "USA Today" best seller list. [END] 
Answer: 
Fifty Shades Darker
Fifty Shades Darker