A slightly surreal-comedic episode, but a bit daft, really. If any episode deserves the tag of "comic-strip", it's this one. In fact under close inspection it just doesn't stand up. Lawson's escape from the hospital is actually witnessed by a member of staff who clearly takes no action, let alone inform his superiors. When Bodie and Doyle finally catch up with the Colonel, they leave him alone, despite the fact he is clearly deranged and - as per the main premise of the story - the authorities are concerned he may reveal NATO secrets if captured by enemy agents. The world's most toxic gas is "secured" in little more than a padlocked shed!

Stephen Greif, unusually, appears in little more than a cameo role.

The Lawson character is, of course, a cariacature of the role. Whether this makes the episode comedic or comic-book is a debateable point. The same can be said of the Brigadier character to an extent. I wonder if Ranald Graham had a grudge against the Army?!

I enjoyed the pub scene, though - "You see what's wrong? They don't stand. It's their own National Anthem and not one of them stood! What we're going to fight for it this country's soul!"

The attack on the research base was over-long, corny and lacking in directorial flair. Below-par editing, there.

The chap playing the excitable professor over-acts all the way through.

The best bit comes at the end where the lads, as usual, save the day in fine style, though it's still a bit of an anti-climax.

Overall, despite some good individual scenes and bits of dialogue, the episode as a whole just doesn't work. It has an interesting central idea - that of a high-ranking officer becoming disillusioned to the point of mental incoherency - but its plotting and execution seem to have been bashed together far too hurriedly. Although Ranald Graham injects some humour into the proceedings, it's often funny for unintentional reasons. All credit, then, to Michael Culver who keeps the Lawson character just the right side of straight-faced barminess.

"He wants the National Anthem played on Radio Two... on the hour, every hour.... forever!"

Lawson's psychiatric hospital is actually Haberdasher Aske's School in Elstree (Thanks to Tony Mackay).

Lots of filming in the village of Batford, near Harpenden. Lawson marches through Sauncey Woods and Batford Ford (pictured here) on his trek to Len's place. Bodie and Doyle drive their Capri through the latter though it is actually quite deep, so metal ramps were hidden just below the waterline.

The Batford Forge which Len works at was a real location but has sadly been demolished and replaced by houses in the last few years. (Many thanks to Brigitte McKnight for Batford info and pic)

Tony Woof thinks the CI5 HQ in this episode might have been in the Wembley Park Drive, Wembley area.

Bob Rocca suggests that Lavinia Lawson's house could be in North Mymms Park, Welham Green, a few miles north east of Borehamwood.

Just north of Slough is Fulmer Grange, Wexham which was used as "Marston Dale" warfare research centre. At the time (1981) it was actually a training centre for concrete technology - the Cement Asscociation's June newsletter carried some pictures of the filming. Nowadays it is apparently run as a college for Japanese students, Teikyo School.

Tug gives the package to the passer-by in Whitehall, SW1.

Lawson sets up his remarkable mirror apparatus in Battersea Park.

From fan Les Martin:

"I was an extra on the episode. At the time I was with the Territorial Army ('C' Squadron, Royal Yeomanry) and we were asked to supply a vehicle for filming. The "Tank" which you refer to was in fact a Fox armoured car Combat Vehicle Reconnaissance Wheeled. We spent all day filming in Battersea Park. My brother was the driver of the vehicle (Keith Martin) and I was the commander. I remember the filming well: we had about five takes when Martin Shaw jumped on the back of the vehicle, but he kept missing his foot-hold and falling. On the one they kept in, it was me that fell over at the end of the shot and fell on my backside!

"We were also in the respirators in the reflection of the mirror device, at the same time standing at the back of the 4-tonner lorry and we also ran in at the end. But the best bit was after filming was when we drove back to the studios and had a good drink in the bar (not the driver), then on the way back, all the fuses blew on the vehicle (no lights), and we had a police escort from one side of London to our base in Croydon.

"It was great fun and whenever I see The Professionals on TV, I think of the day we filmed and the fact they used about 10 secs of our contribution. Great memories."

Michael Angelis has had parts in several classic TV series over the last thirty years. First coming to prominence as rabbit-loving Lucien Boswell in Carla Lane's popular 70s sitcom The Liver Birds. Then on to Alan Bleasdale's unforgettable Boys from the Blackstuff and GBH. Also starred as a copper not averse to giving villains a bashing in a very fine episode of Between the Lines. More recently seen in the very welcome revival of Auf Wiedersehen, Pet.

Michael Culver had previously been seen in the New Avengers episode 'Hostage'. He guested in many cult 70s shows such as Doomwatch, The Persuaders, Public Eye, Van Der Valk, Clemens & Fennell's Thriller, The Sweeney, Space:1999, Shoestring and Minder. You might spot him in The Empire Strikes Back. Didn't appear to do much TV work in the 1980s and was most recently a regular in the unlikely Derek Jacobi vehicle Cadfael. (Actually was this series any good? The IMDB describes it as "A Crusader-turned-Monk uses his botanical knowledge to solve mysteries in the old Norman England village of Shrewsbury" As you do.)

Stephen Greif was another New Avengers guestee. He is, of course, better remembered as the first actor to play Travis in Blake's 7 but had previously played gangster Harry Fenning in popular sitcom Citizen Smith. Still a very busy actor today.