The color master tape of this episode was wiped by the BBC in the 1970s and the BBC only held a 16mm black and white telerecording. The episode remained only in black in white until the 1990s, when the color signal from a domestic NTSC recording and the black and white telerecording were used to create a new color master on D3 digital tape.
This episode was watched by 8.2 million viewers on its original transmission.
First of Two Pertwee era serials that Geoffrey Palmer has small roles in plus he is one of 39 performers to have acted in both the 20th Century series and the 21st Century series.
Richard Steele returns to the series as the hapless Sgt Hart just two stories after his previous role in The War Games . Plus he has acted in both the Colour and Black and white era of Doctor Who.