The Time Traveler's Wife

The Time Traveler's Wife was a popular science fiction book. River Song once read it when the Eleventh Doctor returned from a series of errands, ironically. (COMIC: Take a Bow (Tie))

The Twelfth Doctor later kept a copy of The Time Traveler's Wife in one of the bookcases in his TARDIS. He hid a TARDIS key within its pages. (TV: Dark Water)

Behind the scenes
The novel was published in the early 21st century and written by Audrey Niffenegger. Steven Moffat acknowledged it among his inspirations, especially for The Girl in the Fireplace.