Death in the Clouds
From Tardis Wiki, the free Doctor Who reference
Death in the Clouds was a murder mystery novel by Agatha Christie which was first published in 1935. It was one of Christie's Hercule Poirot novels.
Inside page noting date of publication of Death in the Clouds as 5,000,000,000 (TV: The Unicorn and the Wasp)
Part of the novel's plot (involving a wasp) may have been subconsciously influenced by an adventure Christie shared with the Tenth Doctor and Donna Noble. It was 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. (TV: The Unicorn and the Wasp)
File:Doctor Death in the Clouds.jpg
The Doctor holding his copy of Death in the Clouds (TV: The Unicorn and the Wasp)
