The Doctor first met the Great Intelligence in his second incarnation in the story The Abominable Snowmen: Episode One (1967). He battled against them again in the London underground in The Web of Fear: Episode 1 (1968). A map of the London underground appears on the top of the lunch box The Doctor gives Dr. Simeon.
Clara's introduction to the TARDIS introduced two novel effects for the show. The first was a single-shot camera tracking from a few feet away from the TARDIS to its interior, with the implication of the TARDIS' trans-dimensional nature shown to the audience. In the following shot, the camera does a complete circle of the TARDIS console, an effect not seen since the early days of the show. Saul Metzstein wanted to include this shot to further emphasize the "bigger on the inside than the outside" nature of the time machine.
When The Doctor is introduced as Sherlock Holmes, the music mimics the style of David Arnold's music from the show Sherlock (2010) which is also by Steven Moffat. However, due to copyright reasons (they would have had to pay Arnold), the tune is not quite the same.
There are Sherlock Holmes connections:
- Dr. Simeon suggests that Arthur Conan Doyle based Sherlock Holmes on Madame Vastra. Richard E. Grant had previously played Holmes in The Other Side (1992), Mycroft Holmes in Sherlock (2002) and Jack Stapleton in The Hound of the Baskervilles (2002).
- The Doctor impersonates Holmes. At the time, Steven Moffat was overseeing Sherlock (2010), which Matt Smith had previously auditioned for. In addition, the incidental music in the scene is similar to the Sherlock theme.
- Ian McKellen would later play the lead role in Mr. Holmes (2015).
The idea of Strax serving as "a grumpy butler" to Vastra was derived from comments Dan Starkey had made in the August 2011 issue of Doctor Who Magazine.