• title card: The Deadly Air superimposed on a close-up of Dr Karswood
  • publicity still: Steed chats up Barbara
  • publicity still: Steed and Dr Keel question Dr Harvey
  • publicity still: Heneager attacks Armstrong
  • publicity still: Dr Kilbride takes time out from his yoga to talk to Dr Keel
  • Steed, thinking himself infected and self-quarantined, peers out the porthole as Dr Chalk shows him the real ampules have been returned and he is safe to come out

Series 1 — Episode 24
The Deadly Air

by Lester Powell

Production completed: 7 September 1961. First transmission: 16 December 1961

TV Times summary

Keel and Steed face a murder weapon which cannot be detected until it has struck

The following episode summary is written from the published synopses, other previously published material and Leonard White’s scrapbook of notes and Tele-Snaps as this episode is now lost. There may have been changes made during filming. I have made a few assumptions, marked with footnotes, to try to explain gaps and plot holes. My breaks in the acts are based on when significant cliff-hanger events or changes of location happen and may not be completely accurate.

Plot summary

When several experiments with a new vaccine go wrong, Steed and Dr Keel investigate. One of the scientists, Heneger, is sabotaging the project and a potent airborne virus nearly kills the Avengers. As Keel interrogates Heneger for the truth, Steed is discovering that Dr Craxton is the real mastermind. Steed is convinced that Craxton has fatally poisoned him, until it is revealed that the lethal vaccine had been replaced by water as a security measure.

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Prologue

At Truscott Research Laboratories, Barbara Anthony (Ann Bell) and Dr Philip Karswood (Michael Hawkins) are working in the lab, writing up their findings and batch parameters as they prepare vials of a new vaccine for testing. Barbara leaves while Dr Karswood carries the precious vials carefully out of the lab.

Act 1

Dr Karwood arrives at the laboratories’ centrifuge room where Dr Heneager (Keith Anderson) is working. Karswood places the vials inside the centrifuge, showing Dr Heneager the desired pressure and speed levels required for this test. He discusses the procedure and expected outcomes with Dr Heneager, excited that their research could lead to a medical breakthrough. However, after Dr Karswood returns to the lab he shares with Barbara, another person wearing protective gear enters silently and attacks Dr Heneager, pressing a pad soaked in chloroform against his nose and rendering him unconscious. With Heneager taken care of, the assailant changes the pressure of the centrifuge, rendering the vaccines unviable.

John Steed (Patrick Macnee) and Dr David Keel (Ian Hendry) arrive at the research facility and don protective equipment before heading into the labs. The head of the research facility, Herbert Truscott (Richard Butler), arrives to check on his team. He’s not taking an active part in these experiments so hasn’t bothered to wear his PPE but is concerned the attack will put them behind schedule. He tells his staff that Steed and Dr Keel will be investigating.

Steed zeroes in on the pretty Barbara, being the only female scientist at the centre, and makes small talk while subtly asking her about suspicious activities at the lab. Unfortunately, she hasn’t noticed anything herself, but there have been several unexplained setbacks to the vaccine research, and now the attack on Dr Heneager that ruined their latest batch - which they were sure would work. Dr Heneager meanwhile is in another corner with Dr Owen Craxton (John Stratton), who is ribbing him about being easily overcome.1 Heneager tells Dr Keel he can’t tell him anything about his attacker as he was taken by surprise from behind. The head of research, Dr Hugh Chalk (Allan Cuthbertson), clipboard in hand, is also unable to furnish Dr Keel with any useful information but wants to press on with the research.

Thwarted in their initial enquiries, the Avengers take a break, Steed heading off to telephone One-Ten (Douglas Muir), who tells him to hurry up with his investigation; the vaccine research is vital to national security.2 Carol Wilson (Ingrid Hafner) has arrived and meets Dr Keel in the staff canteen, giving him a huge pile of vaccine textbooks to skim through.

After the tea break, Truscott reconvenes his research team - Doctors Chalk and Craxton have agreed they must proceed with another test and Dr Karswood, feeling guilty about not having directly supervised the last test, insists on taking the lead role in the new run and will enter the test chamber. He starts distilling some of the chemicals required at his bench. Dr Chalk and Barbara are impressed by his dedication but somewhat concerned as well. Barbara reminds Karswood he’s not to blame and should not shoulder the whole burden himself.3

Dr Keel put on some protective clothing and helping Dr Heneager inject a guinea pig to ensure the vaccine will be safe.4 He asks Heneager about the procedure and Heneager tells him that is something goes wrong, Karswood could die! Dr Karswood enters and scoffs at this nay-saying and orders them out of the test chamber. The chamber is hermetically sealed behind them, Dr Heneager turning on the pressure controls after leaving as Karwood had shown him before.5

Inside, Dr Karswood dons a face mask and prepares a test tube with the distillate. Steed and Dr Keel have skived off to the canteen for a light supper with Barbara and a cigarette. Back at the test chamber, Karswood is startled to find his breathing becoming laboured. He tears of his mask and blunders out of the test room,6 gasping, then he collapses to the floor...

Act 2

The alarm is given and pandemonium breaks out, the other scientists hurriedly putting on facemasks and entering the test chamber. Dr Karswood is whisked away to the medical wing of the facility and put in an Iron Lung to assist his breathing while he is examined by Dr Harvey (Cyril Renison) and nurse (Susan Castle) assisting. After trying to save Karswood for some time, Dr Harvey turns to Steed and Keel, who have been waiting in the corner of the ward, and regretfully announces that Karswood had not responded to treatment and is dead. He tells them his lungs were contaminated by the virus they were trying to vaccinate against. Dr Chalk goes to break the news to Barbara, who is weeping quietly to herself in the laboratory.7

Steed is perplexed how this could have happened - the vaccine shouldn’t be as virulent as the virus itself - and enlists the help of Ken Armstrong (Anthony Cundell), the engineer who supervises and maintains the facility’s machinery. They inspects the testing chamber and equipment and in one of the inlet air ducts they find fine splinters of medical grade glass on the impeller blades. Steed enters the chamber where Dr Keel is preparing to test the vaccine on a guinea pig.8 As Steed holds the rodent still, Dr Keel carefully injects the vaccine into the guinea pig, and they both fail to notice that the streamers hanging from the air duct start billowing again as someone has restarted the fans...9

Ken has gone to the lab to commiserate with Barbara, and hesitantly conveys the suspicions of sabotage. He promises to uncover the killer and she thanks him bravely, holding back the tears. Ken departs and re-enters the corridor outside the test chamber. He goes to inspect the duct for more clues and realises the fans have been restarted. He goes to turn them off and is attacked from behind, stabbed by Dr Heneager with a hypodermic syringe10 and left to die... but, making a monumental last effort, Ken reaches up and turns the fans off, releasing the test chamber door. Keel and Steed, who had been trapped in the test chamber by the door slamming shut with the change of pressure, rush out and find Ken dead on the floor. As Dr Keel examines the dead man on the floor, Steed checks the intake fan and finds an unbroken phial of liquid taped to one of the blades. The phial is analysed and discovered to be the raw virus, 100 times more virulent than the vaccine.

Act 3

Steed makes another call to One-Ten who tells him to get in touch with the eccentric virologist, Professor Kilbride,11 upon whose work Truscott’s team have expanded. Dr Keel worked briefly with Kilbride at a London hospital so goes to visit him12 but is astonished when he arrives at his house and finds that Professor Kilbride (Geoffrey Bayldon) is now a loin-cloth wearing Yogi, sitting on his bed, cross-legged and half-naked. Kilbride says he has turned his back on Western medicine, wanting nothing to do with his past work. When he hears of what has happened at Truscott Research Laboratories, the Professor relents and agrees to help. Dr Keel hands him two phials to analyze, the one from the fan and another containing the vaccine.

Back at the lab, Barbara goes to secure the remaining phials of raw virus now they know how lethal they are but then she, too, is chloroformed and the deadly phials are stolen. Unaware of developments at the lab, the Professor has got straight to work, putting on a dressing gown as he inspects the samples, trying to determine their origin. He finds something interesting and calls the lab but Steed and Dr Keel are busy questioning Barbara, so Dr Heneager takes his call...13

Barbara can’t remember anything about the attack but tells them about the phials being stolen. They realise the Professor may now be in serious danger. A short time later, Dr Heneager arrives unexpectedly at the Professor’s house and asks him for his report on the phials. The professor is cagey, unsure of this stranger - and rightly so, as he holds a hypodermic behind his back, ready to kill again if necessary! Dr Keel arrives in the nick of time, having been sent back immediately once Steed realised the danger the Professor was in, and throws himself at Dr Heneager, disarming and subduing him. Chastened, Heneager confesses to the murder of Armstrong but says he wasn’t behind the plot - Dr Craxton is the mastermind who staged the first attack on Heneager, and is Dr Karswood’s murderer.

Dr Craxton is in the corridor as Steed returns to the test chamber to search for more clues, unaware of the scientist’s guilt while Dr Keel is racing back to the research lab. Craxton locks Steed in the isolation lab and starts the fans, another of the phials stuck to the impeller blades. Steed hears the fans and rushes to the door, peering despairingly through the reinforced porthole; the glint of glass splinters on the floor confirming to him that he’s been exposed to the contents of one of the deadly phials...

Steed can only watch on helplessly as Dr Keel and Dr Chalk suddenly appear in the hallway and apprehend the surprised Dr Craxton. They turn off the fans but Steed refuses to come out, daring not to open the door lest they be infected with the virus too. Keel tells him Heneager confessed everything - Craxton had planned to sabotage the vaccine’s research to discredit it, then release it onto the market himself14 under a different name and formulation to make millions. Dr Chalk tells Steed to come out of the test chamber but he still refuses - until Dr Chalk holds up the remaining real phials, and tells him that those stolen from Barbara were harmless and only contained distilled water! Dr Truscott had swapped the phials without telling anyone as he no longer knew who to trust at the research facility. Steed emerges from the lab, relieved that he will live.


  1. Well, maybe. There’s a Tele-Snap that shows them together and Craxton has a bit of a smirk on his face. Of course, it’s possible it’s foreshadowing of the climax of the plot and he’s smug about their deception being successful.
  2. We don’t have a script to be sure about this interaction but One-Ten looks grim, as always, and this is the sort of thing he always tells Steed.
  3. A series of Tele-Snaps shows Karwood using his scientific equipment and then close-ups of Chalk and Barbara looking concerned, then one last one where Barbara seems to be imploring someone.
  4. There’s a Tele-Snap and several publicity still showing Heneager and Keel with the guinea pig; see also note 8 below.
  5. There’s the suggestion in Two Against the Underworld (Hidden Tiger/Lulu hardback, 2015, p. 408) that the Tele-Snap showing the controls being set is another sabotage attempt but I think it’s reinforcing that Karswood is now effective trapped in the chamber.
  6. Despite this being a shocking breach of scientific protocol, the test room door is clearly in the background of a publicity still of this scene.
  7. There is a very moving sequence of Tele-Snaps that shows the action from Dr Karswood being put in the iron lung until Dr Chalk goes to speak to Barbara, who is looking very sad and lonely in the lab.
  8. Dave Rogers stated in The Avengers by Dave Rogers (ITV Books/Michael Joseph 1984 paperback reprint, p. 22) “when a monkey is injected, it remains healthy” but a Tele-Snap shows Steed holding a small animal as Keel injects it. There’s also another Tele-Snap and series of publicity stills (see note 4 above) that show Dr Heneager opening a guinea pig cage and Dr Keel injecting it, from an earlier sequence.
  9. There is a Tele-Snap showing the billowing streamers hanging from the air duct.
  10. The Avengers by Dave Rogers (ITV Books/Michael Joseph 1984 paperback reprint, p. 22) says Armstrong was shot but Heneager appears to be holding a hypodermic in the Tele-Snaps and publicity stills of the scene, and again later when he menaces Professor Kilbride.
  11. The Avengers by Dave Rogers (ITV Books/Michael Joseph 1984 paperback reprint, p. 22) simply says “Steed seeks the help of Professor Kilbride”. Two Against the Underworld (Hidden Tiger/Lulu hardback, 2015, p. 410) suggests that Steed already knows Professor Kilbride and rang him directly but, again, I thought it likely that One-Ten or maybe Truscott would tell him.
  12. Dr Keel always knows the other doctors they meet and has always worked with them in a hospital, so it seemed more natural that Keel would have the connection with him - and explain why it’s Keel who visits Professor Kilbride and just lets himself into the professor’s house.
  13. The Tele-Snaps don’t show who answers the Professor’s call nor do they show Steed and Keel questioning Barbara but this explains why none of them answered the phone and fits the overall narrative of the pictures. Of course, it could have been Craxton who answered the phone and sent his henchman to deal with the professor.
  14. A similar plot point occurs in One for the Mortuary.

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