While filming the climax, Barry Letts was misinformed as to the best way to record these sequences, a problem compounded when the film became jammed in the camera. This sorely limited the number of shots Letts could use in the finished programme.
This episode was wiped by the BBC and no copy of it was thought to exist until October 11 2013, when the BBC announced that the episode (along with the others missing from this serial) had been recovered from a television relay station storage room in Nigeria. It was subsequently restored to the BBC television archives and released on iTunes.
This episode takes place in 2018.
This episode was watched by 8.3 million viewers on its original transmission.