Master gadget maker Fitch pulls a tubular weapon; Steed tells Emma it is a bicycle pump gun, the Maquis used then during the war. Fitch says he invented it. The WW2 European resistance fighters used many peculiar weapons. There were lethal and nearly silent air rifles you pressurized with a bicycle pump, rifles made from bicycle pumps, rifles made to look like pumps, and of course the high explosive rats. Fitch may have worked for the Special Operations Execute which designed and supplied such devious weapons.
At about 19 minutes, Steed and Peel visit the Boardmans' flat. Background music is playing - a rather laid back lounge version of the main theme.
About 4 minutes in, Steed mentions that his uncle's watch was dented by a Canadian mule. There are several references to Canada in the series; prior to joining The Avengers, Patrick Macnee was based and worked in Canada.