The second of three appearances by John Mills, the others being S2 E3, Galloping Foxley (1980), and S5 E3, Operation Safecrack (1982).
The first of two appearances in this second series by John Rees, the other being in S2 E16, The Man at the Top (1980).
The town plan that the 'Umbrella Man' is studying in his hotel room is an actual map of Norwich.