"The Great Detective" is a Doctor Who mini-episode, or "minisode" that acted as a prequel to the events of the Christmas special "The Snowmen". It aired as part of the telethon for the Children in Need charity appeal on November 16, 2012. It showed the Eleventh Doctor, played by Matt Smith, retired from saving the Earth, along with the efforts of Madame Vastra, (Neve McIntosh) Jenny Flint (Catrin Stewart) and Strax (Dan Starkey) to bring him out of retirement.
The "minisode" begins with an introduction, where Matt Smith mentions the Doctor said his goodbyes to Rory Williams and Amy Pond (also known as Amelia Pond) in the prior episode "The Angels Take Manhattan". While Matt claims that Amy was the woman who would never be replaced in the Doctor's two hearts, the camera pans back and reveals Jenna-Louise Coleman, the actress who would play the new regular companion, Clara Oswald, from "The Snowmen" onwards. Jenna assures Matt that "she" (referring to Amy's actor, Karen Gillan) wouldn't be watching as she was in Los Angeles at the time of the "minisode"'s airing.
Plot
A narrator (voiced by Mark Gatiss) refers to the Victorian era's "Great Detective": a lizard woman from Paternoster Row in London called Madame Vastra (Neve McIntosh), and her adventures with her "assistant", Jenny Flint (Catrin Stewart) and their ugly henchman, Strax (Dan Starkey). The narrator alludes to a fourth member of the "Paternoster Gang" – the Eleventh Doctor (Matt Smith) – whose assistance was sought after only in emergencies. Vastra reports to the Doctor that a meteor shower has a slight possibility of alien intervention. Jenny told the Doctor about a professor with a giant drill threatening to split the Earth open, only he didn't have a giant drill and was singing and drunk. Strax claimed to have declared war on the Moon and demands that it's time to act against the "Moonites".
After a long pause, the Doctor reminds the gang that he has retired from responding to emergencies. Jenny tries telling him about a man with an invisible wife, and wishes the Doctor a Merry Christmas as he walks away. She and Vastra realise that the Doctor actually meant it when said he was retired.