Gareth Roberts, a self-confessed fan of Christie's works, previously wrote the pseudohistorical story "The Shakespeare Code". He is reported to have based "The Unicorn and the Wasp" on his favourite Christie works: "Crooked House", which focuses on secrets within an aristocratic society, and the 1982 film adaptation of "Evil Under the Sun".
The story’s title was deliberately chosen to sound "vaguely Christie-ish", even though Christie never used 'the blank and the blank' construction. In writing this story, Roberts aimed to make it a "big, fun, all-star murder mystery romp".
The Doctor previously stated in the story "The Sound of Drums/Last of the Time Lords" that he would love to meet Agatha Christie and in this story he says 'I was talking about you the other day'.
Agatha Christie really did disappear for ten whole days in 1926 when she drove away during the night and was found ten days later in a hotel in Harrogate - although her car was found in a chalk pit, not next to a lake. Some claim she had suffered a breakdown, while others said it was all a publicity stunt. Also the Harrogate Hotel where The Doctor leaves Agatha is fictitious. In actuality, the hotel where she was found was the Swan Hydro (now the Old Swan Hotel), a somewhat less imposing building than the one depicted in this story. After a hugely successful career and a very happy life Agatha died peacefully on 12 January 1976.
According to Guinness World Records, Agatha Christie is the best selling novelist of all time. She also comes second to William Shakespeare as the best selling writer of any kind.
Throughout this story Agatha Christie's book titles were mentioned just in general conversation. For example "Murder on the Orient Express" and "Miss Marple" are mentioned by Donna Noble, both in front of Agatha Christie who had not, at the time of this story, written them.
Donna mentions that meeting Agatha Christie during a murder mystery would be as preposterous as meeting "Charles Dickens surrounded by ghosts at Christmas", making a reference - unbeknown to her - to The Doctor's previous adventure with Charles Dickens in "The Unquiet Dead".
Fenella Woolgar, who plays the part of Agatha Christie, previously appeared alongside David Tennant in the Stephen Fry film "Bright Young Things". Funnily enough, her character in that was also called Agatha.
Christopher Benjamin, who plays Colonel Hugh, previously appeared in the 1970 Third Doctor story "Inferno" and the 1977 Tom Baker story "The Talons of Weng-Chiang".
The Colonel's reference to Mafeking relates to a famous siege in Africa during the Second Boer War. It lasted 217 days, from October 1899 to May 1900. The Doctor implied that he was present at the siege in both episode 8 of 1966's "The Daleks' Master Plan" and in the 1978's "The Invasion of Time".
Possibly because this is the first story Catherine Tate recorded since her debut in "The Runaway Bride", Donna repeats the high-pitched squeak of surprise first heard when she is transported from her wedding to the TARDIS at the beginning of that story.
The Tenth Doctor has now kissed (or been kissed by) all his female companions. Cassandra (in the body of Rose) kissed him in 2005's "New Earth", he kissed Martha Jones in an attempt to confuse the Judoon's genetic scanners in 2007's "Smith and Jones", Astrid planted one on him in 2007's "Voyage of the Damned" - and now Donna uses a kiss to shock his system and reject a potentially fatal dose of cyanide.
Cyanide has been used throughout history as a poison. The Fourth Doctor even used a gaseous form of it in 1976's "The Brain of Morbius".
When Donna opens up Lady Eddison's sickroom, she finds a large teddy bear on the bed. The room itself had been locked and left undisturbed for 40 years before the 1926 setting of this story. The teddy bear was not invented until after 1902, when the cartoon of American president Theodore Roosevelt which inspired it was first published. Therefore it follows that it would have been impossible for a teddy bear to have been placed in the room in 1886, making its appearance, in this story, an anachronism.
At the end of the story, the Agatha Christie novel "Death in the Clouds" is produced from a chest in the TARDIS – The cover of which portrays a large wasp.
When looking through his trunk to find his Agatha Christie book, The Doctor unearths a Cyberman chest-plate and the crystal ball in which the Carrionites are trapped, in "The Shakespeare Code".
The end of this story contains a trailer for the first episode of the next story "Silence in the Library/Forest of the Dead".
Following on immediately after this story, on BBC3, was the seventh chapter of the fourth series of Doctor Who Confidential, "Nemesis" presented by Anthony Head.
The first story Catherine Tate recorded since her debut in "The Runaway Bride".