This is the first episode in which pursuit ships and Mutoids are seen: They had been first mentioned in Cygnus Alpha (1978) and Seek-Locate-Destroy (1978) respectively.
This is one of two episodes to not have music by Dudley Simpson. Director Douglas Camfield bore a personal grudge against Simpson and refused to work with him, and so used library music. The tracks concerned are 'Countdown' and 'Space Panorama' from the library album 'Terrestrial Journey' and 'Genesis' by John Cameron.
This episode has similarities to Arena (1967) which itself is a credited and paid for adaptation of the short story "Arena" by Fredric Brown.
Including main, guest, and background characters, this is one of only two episodes in which nobody dies.