Private Madness, Public Danger

Charles Nesbitt is an expert on chemical warfare, and he has decided to use that knowledge to hold London to ransom. His plan is to poison the city's water supply with a lethal hallucinogenic drug, and his way of advertising the threat is a series of small demonstrations outside the capital. Each one is a warning aimed at the local authorities and, pointedly, at CI5.

The hunt that follows is the real subject of the episode. There is no bomb to defuse and no deadline to count down to. There is just a clever man with a grudge and a working knowledge of poison, which is a nastier combination than any amount of explosives. The demonstrations are lurid enough to make the papers, and that is the point: he wants to be noticed, and he wants to be feared. Keith Barron plays Nesbitt with the quiet satisfaction of someone who believes he has thought of everything, and watching CI5 pick its way towards him through his contacts and his warnings provides most of the fun. The threat stays off screen for long stretches, and the show trusts the audience to find that more frightening.

Brian Clemens and Anthony Read wrote it, and Douglas Camfield directed. Gordon Jackson's Cowley, Martin Shaw's Doyle and Lewis Collins's Bodie do the chasing, with Donald Douglas as Eric Sutton, Di Trevis as Susan Fenton, Angus MacKay as Gerald Harvey, Trevor Adams as Benny, Christopher Ellison as Biggs and Peter Penry-Jones as Cummings. Ellison would spend the eighties as Frank Burnside in The Bill, which makes his small part here a footnote worth catching.

It works as a first episode because it takes the danger seriously without taking itself too seriously. And the fear at its centre, the worry about what goes into the water everyone drinks, has not aged a day.