This episode is one of two (the other being Attack on Cloudbase (1968)) to feature all of the regular characters, although not all have speaking parts.
One of the rare occasions where Colonel White is seen wearing his colour-coded Spectrum hat (albeit the same white hat is worn by Spectrum Security Officers whom had made many appearances by now).
This is the last of three episodes in which dialogue indicates that events from the story - in this case, the ending - take place on 10 July (the birthday of series writer/script editor Tony Barwick), the others being Winged Assassin (1967) and Treble Cross (1968). As a result, fans of the series observe 10 July as "International Captain Scarlet Day".