First episode to cast Diana Rigg as Mrs. Emma Peel. Eleanor Bron turned down Emma Peel and the role was taken by Elizabeth Shepherd, who was replaced by Diana Rigg midway through filming her second episode. (Both the first and second episodes were subsequently reshot with Rigg.)
First episode introducing the now famous theme song composed by Laurie Johnson. This catchy tune was also the base for the theme of the TV series The New Avengers (1976) and again for the movie The Avengers (1998)
First episode in which Mr. Steed demonstrates that his bowler hat is reinforced with steel (twice).