The series centred on a pair of interdimensional detectives (Sapphire and Steel). Very little was given away about them (even the job titles above are a best guess) but they appeared to be engaged in ensuring time runs smoothly and nothing untoward happens with time itself. Time is often characterised in the show as being an actual entity - although always 'off stage'.
The episodes were typically cryptic and raised more questions than they answered. There's a lot of debate amongst sci-fi buffs as to their meaning. However, they were all spooky and the programme's use of simple but effective staging and very few special effects somehow add to this.
Sapphire and Steel were assisted by other operatives, including Lead and Silver. All operatives have special powers. Sapphire can manipulate time in small ways as well as divine the age of an item by touching it, while Silver is good with electronics and gadgets. Steel can freeze himself to absolute zero which gives him the ability to destroy 'ghosts' (people who are remnants of time). Steel also possesses immense strength- in adventure 3 he ties knots in lift cables to prevent the lift being used. Sapphire and Steel aren't necessarily 'good guys' - their prime concern is to ensure time runs smoothly rather than ensure the safety of humans. It's not even clear if they're actually human themselves.
Each series of adventures would start with Sapphire and Steel materialising out of thin air (although often they were already present when the show started), and usually they would investigate and mingle with various humans, although it was nearly always the location the humans were in which was of the most interest - an old house which dates back to the English Civil War, an abandoned railway station, a motorway cafe, etc.
The shows began with the words: "All irregularities will be handled by the forces controlling each dimension. Transuranic heavy elements may not be used where there is life. Medium atomic weights are available: Gold, Lead, Copper, Jet, Diamond, Radium, Sapphire, Silver and Steel. Sapphire and Steel have been assigned."
Yes, it was a very pretentious show, but also one that wasn't scared of being intellectual as well as hugely entertaining - this was popular prime-time viewing across the UK yet it raised questions about time and the universe around us. The series is available on DVD.
The six adventures were: