Death in the Clouds

Death in the Clouds (also published under the variant title Death in the Air) was a murder mystery novel by Agatha Christie which was first published in 1935. One of Christie's Hercule Poirot novels, part of the novel's plot (involving a wasp) may gave been subconsciously influenced by an adventure she shared with the Doctor and Donna Noble. It is one of a number of Christie's works to be preserved through human history, with an edition owned by the Doctor carrying a publishing date of the year 5 Billion. (DW: The Unicorn and the Wasp)

Exactly when the Doctor obtained his copy is unknown, though it may have been around the time of his visits to New Earth with either Rose Tyler (DW: New Earth) or Martha Jones (DW: Gridlock), both of which took place sometime after the year 5 billion.