Director John Hough confessed that the entire population of the city of St Alban cooperated to the making of the episode,so that no one appeared in the streets or behind windows during the shooting, which began very early in the morning, on Sunday only.
Whilst the majority of the filming took place on location, some scenes were filmed on the standing outside set at Associated British Studios, Borehamwood. Most notably when Steed and Merlin are leaving the bank, the house on the right is Simon Templar's house from The Saint.
The haunting music that plays as Steed and Merlin wander the streets was played on a rare musical instrument called a glass harmonium.
As another episode "The Curious Case of the Countless Clues", where she suffered from a broken ankle, Tara is nearly absent during the whole story because of a sleeping gas, except for two brief fights.
As Steed and Merlin wander the streets, Steed is seen without his trademark umbrella.