This marks the first episode where the series favorite Brigadier Lethbridge-Stewart was introduced as a Brigadier, a promotion from Colonel.
From dialogue given by the Brigadier that this story takes place 4 years after the yeti incident (a reference to The Web Of Fear) which was set in 1975 (from Dialogue in that story stating it took 40 years after The Abominable snowmen which itself was set in 1935) that the dating of this story is in 1979.
This episode was watched by 7.1 million viewers on its original transmission.
The record that Isobel plays for Zoe on the old gramophone which she says she bought off a barrow in the Portobello Road is Henry Hall and his Orchestra's 1932 recording of "The Teddy Bear's Picnic" - a recording that was used by the BBC for over 30 years to test the frequency response of their audio equipment .