The Fourth Dimension
The Unicorn and the Wasp
Agatha Christie really did disappear for ten whole days in 1926, although her car was found in a chalk pit, not next to a river. Some claim she had suffered a breakdown, while others said it was all a publicity stunt.
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.
Bright Young Thing
Fenella Woolgar previously appeared alongside David Tennant in the Stephen Fry film Bright Young Things. Funnily enough, her character in that was also called Agatha.
The Talent Of Weng Chiang
Christopher Benjamin previously appeared in Doctor Who adventures Inferno (1970) and The Talons of Weng-Chiang (1977).
The Sidecar cocktail ordered by Donna is traditionally made with cognac, orange liqueur and lemon juice. A Harvey Wallbanger is made with vodka, Galliano, and orange juice.
What the Dickens?
Charles Dickens? Christmas? Ghosts? It could never happen - except perhaps when the Ninth Doctor and Rose visited Cardiff in 2005's The Unquiet Dead.
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 Volcano (episode 8 of 1966's The Daleks' Masterplan) and in 1978's The Invasion Of Time.
Possibly because it was 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 episode.
Drink And Die
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.
We're Not A Couple
The Tenth Doctor has now snogged (or been snogged by) all his female companions. Cassandra (in the body of Rose) kissed him in 2005's New Earth, he kissed Martha 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.
All About Agatha
Agatha Mary Clarissa Miller was born on 15 September 1890 in Torquay, Devon, South West England. Agatha loved to read and began writing poems when she was a child. During her teenage years they were published in magazines from time to time and were later published under the title The Road of Dreams.
In 1912 Agatha met Archie Christie and they soon married. Agatha became a nurse at the Red Cross Hospital in Torquay. When the Hospital opened a dispensary, she completed the examination of the Society of Apothecaries. Thus began her life long interest in the use of poisons.
During the First World War there were Belgian refugees in most parts of the English countryside. Agatha thought that a former great Belgian policeman, would make an excellent detective for her first novel The Mysterious Affair at Styles. Hercule Poirot was born.
On the 5th August, 1919, Agatha gave birth to her daughter, Rosalind. Also that year the publisher, John Lane contracted Agatha to produce five more books. She went on to be one of the first authors Penguin ever published.
In 1926 Agatha's mother died. In the August, Archie confessed his love for Nancy Neele, who shared his passion for golf and moved out. These events heralded an extremely unhappy time for Agatha. In December, in some desperation, she drove away during the night and was found ten days later in a hotel in Harrogate. Doctors diagnosed that she had simply forgotten who she was. When she had recovered she agreed to divorce Archie.
By 1930, Agatha created a new character to act as sleuth. When she created Miss Marple, it appeared she had produced another popular and enduring character.
Agatha would eventually find happiness when she married Max Mallowan - the world famous archaeologist. Agatha accompanied Max on his archaeological expeditions and became something of an expert on the subject and on the Middle East, as can be recognised in books such as Murder on the Orient Express, Death on the Nile, Appointment With Death and They Came to Baghdad.
After a hugely successful career and a very happy life Agatha died peacefully on 12 January 1976.
You can find out lots more about Agatha Christie at her Official Website. The BBC is not responsible for the content of external websites.
Compiled with the help of Peter Ware and Tamsen Harward of www.agathachristie.com.