The Brigadier receives a telephone call from the Prime Minister and it is made clear it is a woman when he says "Madam". This was a joke from director Douglas Camfield. It is sometimes assumed that this was predicting a general election win for Margaret Thatcher, who had recently been elected Leader of the Opposition when the serial was recorded. However, in subsequent interviews Nicholas Courtney said Camfield had wrongly predicted the woman would be Shirley Williams, who was then serving as Secretary of State for Prices and Consumer Protection in the Labour government.
Features the last Appearance of Harry Sullivan as a regular companion, the reason for his departure is Ian Marter was contracted for a season or a recording block which included this story as it was apart of the previous seasons recording block, and that the character was conceived when the intention was that the 4th Doctor was going to be an older actor, and so Harry was created to handle the action sequences, but with Tom Bakers casting Harry became largely redundant.
The music by Geoffrey Burgon was created by five musicians playing a combination of flute, clarinet, harp, violin, cello, clavichord and percussion.
This episode was watched by 7.2 million viewers on its original transmission.