In the first prequel, “The Great Detective”, the Silurian Madame Vastra (Neve McIntosh), her human wife Jenny Flint (Catrin Stewart), and their Sontaran servant Strax (Dan Starkey), describe some strange phenomena to the Doctor. In the second prequel “Vastra Investigates”, Vastra and Jenny apologise to an officer from Scotland Yard for Strax’s violent tendencies. She mentions in passing that she was woken from a deep subterranean sleep by the construction of an extension to the London Underground. In the third prequel, “The Battle of Demon’s Run—Two Days Later”, Vastra and Jenny convince Strax that he is not dead and invite him to Victorian London. In addition, there is a video somewhere of Strax singing Sontaran Christmas songs.

The Doctor has retired from saving people and uses Vastra, Jenny, and Strax to keep people away while he lives in seclusion literally in the clouds. In 1892, a barmaid named Clara Oswald (Jenna-Louise Colman) follows the Doctor and both are attacked by snowmen made of psychic snow. The Doctor realizes the snowmen are created by Clara’s thoughts and instructs her to think of melting.

Francesca Latimer (Ellie Darcey-Alden) is having dreams about the return of the dead. Clara, also working as her governess, realizes that the pond that contains the previous governess’s body is the only thing still frozen. Looking for the Doctor, she goes to see Vastra, who tells her she will get only one word to attract the Doctor’s attention. She chooses the word Pond.

The Doctor visits the Latimer family’s pond. He realizes that the evil Great Intelligence (Ian McKellen), in control of the snowmen, is using the old governess’s body to create an ice creature. While Clara puts Francesca to bed, the frozen body breaks into the house. Clara is mortally wounded, and the ice governess is shattered.

The Great Intelligence is controlling Dr. Simeon (Richard Grant). The Doctor tricks him into opening up a memory worm, which latches into him. When the worm erases Simeon’s memories, the Great Intelligence will also be erased. Simeon falls dead. Outside, a salt-water rain is falling, created by the Latimer family crying for Clara. The Doctor realizes that Clara is the same as Oswin, who died on the Dalek’s asylum planet. Since dying twice is impossible, he leaves in the TARDIS to find Clara.

The Great Intelligence controlled the Yeti in the Second Doctor episodes The Abominable Snowmen and Web of Fear in 1967 and 1968. The TARDIS interior was redesigned for this episode and the opening and theme were different. Jenna-Louise Coleman was hired because she could talk faster than Matt Smith. About the only criticisms from reviewers were that Ian McKellen and Richard Grant were under-used as villains. The story was nominated for a Hugo but was beaten out by Game of Thrones. The single camera shot following Clara into the TARDIS was eye-catching. The Doctor impersonates Sherlock Holmes, who had been played by Tom Baker and Peter Cushing, previous Doctors. Steven Moffat wrote the series Sherlock and hinted at that in the music. Matt Smith wore a new Victorian costume. Strax is laugh-out-loud funny.