The Unicorn and the Wasp

194 – "The Unicorn and the Wasp"
Doctor Who episode
The Doctor is confronted with the Vespiform.
Cast
Doctor David Tennant (Tenth Doctor)
Companion Catherine Tate (Donna Noble)
Others Fenella Woolgar – Agatha Christie Felicity Kendal – Clemency, Lady Eddison Felicity Jones – Robina Redmond Christopher Benjamin – Colonel Hugh Curbishly Tom Goodman-Hill – Reverend Golightly Ian Barritt – Professor Peach David Quilter – Greeves Adam Rayner – Roger Curbishley Daniel King – Davenport Charlotte Eaton – Mrs. Hart Leena Dhingra – Miss Chandrakala Alexander McDonald – Footman (uncredited)
Production
Directed by	Graeme Harper
Written by	Gareth Roberts
Script editor	Lindsey Alford
Produced by	Susie Liggat
Executive producer(s)	Russell T Davies Julie Gardner Phil Collinson
Incidental music composer	Murray Gold
Production code	4.7
Series	Series 4
Length	45 minutes
Originally broadcast	17 May 2008
Chronology
← Preceded by Followed by → "The Doctor's Daughter" "Silence in the Library"

"The Unicorn and the Wasp" is the seventh episode of the fourth series of the revived British science fiction television series Doctor Who, which was aired by BBC One on 17 May 2008 at 19:00. Perhaps due to its later broadcast, it received an overnight audience rating of 7.7 million, making it the most successful episode in this series since "The Fires of Pompeii". The episode is a pseudohistorical story set in 1926, in a manor owned by a character named Lady Eddison, which crime fiction novelist Agatha Christie is visiting, and is a comedic episode with a murder-mystery storyline.

The Doctor lands the TARDIS in England in 1926. He and Donna invite themselves to a dinner party hosted by Lady Eddison and her husband Colonel Curbishley. They are thrilled to find one of the guests is Agatha Christie, and the Doctor realises that they have arrived on the day that she will inexplicably disappear for ten days. One of the guests is found dead, and the Doctor uses his psychic paper to convince the rest of them that he is from Scotland Yard and Donna is his assistant. Together with Agatha, he begins investigating. They discover a viscous substance left behind by the killer that the Doctor identifies as morphic residue. He concludes that the murderer is an alien in human form. The Doctor and Agatha question the guests while Donna searches the bedrooms for clues. Donna is attacked by a gigantic wasp, but it escapes through a window before the Doctor and Agatha arrive. The alien kills the housekeeper, and the Doctor, Donna, and Agatha chase it but it returns to human form before they catch it. When they regroup in the study, the Doctor is poisoned with cyanide. His Time Lord physiology allows him to detoxify, with Donna's help. The poisoning inspires him to add pepper to the dinner meal, since the piperine in it would act as an insecticide. As they eat, the guests hear the wasp but the lights in the room are blown out before the alien's identity is revealed. When the lights are restored, they discover that Lady Eddison's necklace has been stolen and that her son Roger has been stabbed to death with a knife.