Fifty Shades Darker by E. L. James

Fifty Shades Darker is the sequel to Fifty Shades of Grey, a 2011 erotic novel by British author E. L. James, writer of the bestselling Fifty Shades trilogy. In Fifty Shades Darker, Anastasia Steele breaks off her relationship with the dark and mysterious Christian Grey, and moves to Seattle to work at a publishing house. However, the two reunite and rekindle their affair. Anastasia must deal with the envy and anger toward the women Christian was with before her, as well as make the most important decision of her life as she learns more about Christian's past and inner demons.
The Fifty Shades trilogy's erotic nature and perceived demographic of its fanbase as being composed largely of married women over thirty led to the books being dubbed "Mommy Porn" by some news agencies. The Fifty Shades trilogy has also been reportedly popular among teenage girls and college women. In March of 2012, a Florida library removed copies of Fifty Shades of Grey from its shelves, citing that it did not meet the selection criteria for the branch and that reviews for the book Fifty Shades of Grey had been poor. A representative for the library stated that it was due to the book's sexual content and voiced that other libraries had declined to purchase copies for their branches. The Florida library later made their copies available to their patrons due to public demand.
The third book in the 50 Shades Trilogy is Fifty Shades Freed. (Summary by Wikipedia)