This episode was wiped by the BBC and no copy of it was known to exist, until December 2011 when it was recovered from a former ITV engineer.
Currently the earliest surviving episode of the Patrick Troughton Era as the previous 11 episodes are not known to survive.
Censor clips were recovered from this episode in 2002, then 9 years later the Episode itself was recovered when returned by a BBC engineer, interestingly it was discovered that the print had numerous cuts, and that the censor clips found previously had been taken from this print of the episode.
This episode was watched by 7.5 million viewers on its original transmission.