A Tale of Two Cities

A Tale of Two Cities was a book that Toshiko Sato once scanned with an alien data scanner salvaged by Torchwood Three. She then attached the scanner to her computer, and was able to read the book on the screen. (TV: Everything Changes)

Behind the scenes
In TV: The Ultimate Foe, Melanie Bush mentions the character of Sydney Carton, implicitly from this book by Charles Dickens, after the Seventh Doctor quoted him.