There's a feast of re-voicing in this episode. Diana Rigg is dubbed by Sue Johnson, Maurice Marsac by Robert Rietty, and Charles Millot by David De Keyser.
Diana Rigg has two short appearances talking to Steed on the phone by using scenes from "The Winged Avenger" and "The Hidden Tiger". So she, her clothes, her flat, nothing seems to have even changed the slightest bit within 10 years.
French title : "Le long sommeil 1".