This is the only episode in the series where Marina can be seen wearing shoes. She is also not wearing her signature green dress.
The first Gerry Anderson production to have a Christmas episode. This would be followed by the Christmas episodes of Thunderbirds (1965) (Give or Take a Million (1966)), Joe 90 (1968) (The Unorthodox Shepherd (1968)) and Terrahawks (1983) (A Christmas Miracle (1984)).
This episode was the 37th episode produced and the 12th broadcast.