This was the fifth episode produced, filmed March 15th to April 1st, 1974 (Breakaway (1975), Matter of Life and Death (1975), Black Sun (1975), and Ring Around the Moon (1976) preceded it) and the first to present Barry Morse's image during the opening titles (taken from "Ring Around the Moon").
This is the last known appearance of Rhonda Parker, who plays the Kaldorian who becomes incinerated (a non-speaking role). Her most famous role was on the last season of The Avengers (1961) playing Mother's able assistant Rhonda, where she never spoke a word in 19 appearances.
After Simmonds swipes Koenig's comm-lock, Zantor says "Then we shall have to make a matrix of the individual you choose". Immediately following is a 43-second deleted scene where Simmonds found himself a laser, but having acquired it ruthlessly, which is why he's seen running with it.
This was the fifth episode in production order, and the first time the Alphans have come face-to-face with an alien race. However, since the producers had intended the episodes to be shown in any order after Breakaway (1975), the script was written to make it seem as though they had encountered aliens previously.