Roger Delgado (Kreer) and Kate O'Mara (Lisa) would both go on to play renegade Time Lords in Doctor Who. Roger was the first actor to play The Master while Kate played The Raini.
First appearance of Father.
The eerie minor key waltz for strings, first heard in "the Joker," is used to good effect in this episode.
Steeds Phone number is WHITEHALL 9819.
Kate O'Mara played Patsy's (Joanna Lumley) sister in an episode of Absolutely Fabulous. Lumley played Purdey in The New Avengers.