Producer-director Patrick Rayner (left) looks on as Holmes examines the wall-safe of Mr James Phillimore, played by guest-star Roy Hudd (right)

The clicking tumblers of the safe's lock are being produced by using a ratchet-driven fishing-reel. Usually a sound-effects specialist takes responsibility for such live "spot" effects, but on this occasion Clive Merrison wanted to create the sounds himself so as to better time them with his spoken dialogue.