Also of note was the casting of the Sontarans. As well as featuring the return of Christopher Ryan in a new role, this episode featured the first Doctor Who appearance of Dan Starkey, seen here as Commander Skorr. Primarily recognised later as Commander Strax, a friend of the Doctor, he would go on to appear in various other roles, several of them also Sontaran, in both the TV series and Big Finish Productions' audio dramas during the years that would follow.