Harry Potter and the Deathly Hallows

The Tenth Doctor told Martha Jones that he cried upon reading the seventh Harry Potter book. (TV: The Shakespeare Code)

Behind the scenes
Harry Potter and the Deathly Hallows, the seventh and final Harry Potter novel, was published on 21 July 2007, three months after The Shakespeare Code's broadcast.

The Doctor's line of "wait till you read book seven" to Martha would appear to indicate that Martha, like the viewing audience at the time, were still awaiting the book's release, despite Martha hailing from 2008.