Production Number: 3367 Tape Number: VTR/ABC/1089 (off-air)
Working Title: 'The Square Root of Evil'


Steed is assigned by one of his superiors, '5', to infiltrate an organisation that intends to flood Britain and Europe with forged bank notes. What is not known is when or how the notes are to be distributed. Another agent, Tobert, had been working under cover among the gang, but he was discovered and brutally murdered. Fortunately, a forger called Riordan is due to be released from prison. '5' knows that the counterfeiters will require Riordan's services and have probably never met the man before, which means that Steed can take his place.

Following three weeks of training in the finer points of forgery, Steed assumes the role of Riordan. He is welcomed by the gang's boss, Hooper, but the second-in-command, a tough customer known as the Cardinal, is far less friendly. The Cardinal is deeply suspicious of the newcomer, and tries various tricks to test his loyalty. Breaking into Hooper's safe late at night, Steed injures his hand and is almost discovered by Hooper and the Cardinal. The injury affords Steed the opportunity to visit Dr Keel, whose assistance may be required later. However, when the order is finally given for the money to be distributed, the gang might not allow Steed to see the doctor a second time...


Read the full story in Two Against the Underworld

The Avengers: Series 1, Episode 3
Production Completed:
Sat 21 Jan 1961 (Live)
Recording Format: 405 Line B/W Video
Archive Holding: DOES NOT EXIST
John Cura Tele-Snaps: Not Photographed
Reconstruction: Not currently possible
Audio Adaptation: Big Finish, 2014
UNITED KINGDOM: Sat 21 Jan 1961
Never transmitted outside the UK


ABC Midlands: Sat 21 Jan 1961, 10.00pm
ABC North: Sat 21 Jan 1961, 10.00pm
Not transmitted
ATV London: Not transmitted
Not transmitted
Grampian: Not transmitted
Scottish: Not transmitted
Southern: Not transmitted
TWW: Not transmitted
Tyne Tees:
Not transmitted
Ulster: Not transmitted
Westward: Not transmitted
Dr David Keel
John Steed
Carol Wilson
Jimmy Bishop
'The Cardinal'
Charles Hooper
Jackie Warren
Steve Bloom
The Secretary
Ian Hendry
Patrick Macnee
Ingrid Hafner
Heron Carvic

Alex Scott
Delphi Lawrence
George Murcell
Vic Wise
John Woodvine (*)
Cynthia Bizeray

(*) Michael Robbins was originally cast as Steve Bloom but was replaced by John Woodvine during the rehearsal period.


Not released.


Stills Gallery


Writer Richard Harris, from a story by John Bryce
Series Theme & Music
Johnny Dankworth
Patrick Downing
Story Editor
John Bryce
Leonard White
Don Leaver

Production Assistant Barbara Forster
Floor Manager Geoff Smith
Stage Manager Nansi Davies
Lighting Director Peter Kew

Technical Supervisor Peter Wayne
Senior Cameraman Michael Baldock
Sound Supervisor Peter Cazaly
Vision Mixer Del Randall

Studio Teddington 2
An ABC Network Production


  • Production Brief... Square Root of Evil was the first of seven consecutive episodes of The Avengers which were produced and transmitted live on a weekly basis up to and including  Ashes of Roses. Notably, during these episodes the focus of the show switches between Steed and Keel each week. In Square Root of Evil, Steed is very much the lead character, with Keel playing a supporting role, not even appearing until the final act. From existing synopses it seems that the next episode, Nightmare, is more about Keel than Steed, while the reverse is true of Crescent Moon. As is well known, Steed is completely absent from Girl on the Trapeze, which seems less unusual when regarded in this context. The spotlight falls on Steed again in Diamond Cut Diamond, on Keel in The Radioactive Man, and then finally on Steed and Carol in Ashes of Roses. This process was intended to take some of the pressure off the two stars, who would effectively be playing a leading role only once a fortnight. After Ashes of Roses, transmission went fortnightly and all episodes were pre-recorded, which meant that 'ensemble' shows with prominent roles for both Hendry and Macnee became more practicable.

  • Contrary to popular belief, the fact that this episode was broadcast live does not mean that it was never recorded. Surviving camera scripts pertaining to the live episodes (those for Square Root of Evil, Girl on the Trapeze, The Radioactive Man and Ashes of Roses) all state VTR (video tape recording) numbers and note that the recordings were to be made from transmission. Additionally, a production memo detailing a proposed 1962 repeat run of Series 1 episodes lists VTR numbers for all of the live episodes, indicating that these recordings were held on tape by ABC as at 30th March 1962.

  • Production correspondence of the time reveals that Richard Harris' script was based on a story by script editor John Bryce. Bryce's involvement appears to have been otherwise uncredited. The document concerned also gives a delivery due date for the script: 27th December 1960.

  • The camera script of Square Root of Evil shows that Bloom was played by John Woodvine, and not Michael Robbins as stated in TV Times and other listings magazines. Many subsequent episode guides have used contemporary cast listings as reference material and this information is now known to have been erroneous. Presumably Robbins became unavailable and was replaced by Woodvine after the magazines (which at the time had print turnarounds of about a fortnight) had gone to press. Robbins, best known for his recurring role in the London Weekend Television situation comedy On The Buses, would eventually grace The Avengers with his presence in Dragonsfield, Mr Teddy Bear and, in the film era of the series, Take Me to Your Leader. Last minute casting changes also occurred in three other Series 1 episodes, Girl on the Trapeze (in which Mia Karam replaced Nadja Regin), The Radioactive Man (in which Arthur Lawrence replaced Gerald Sim) and Tunnel of Fear (in which Anthony Bate replaced Murray Hayne).

  • The camera script also credits Cynthia Bizeray as 'The Secretary' in the cast list, but there is no character referred to as such in the script itself, just 'Girl'. We can only assume that they are one and the same character.

  • Alex Scott's casting as Jimmy Bishop, also known as 'The Cardinal', would seem to have been most appropriate. The character is described as an Australian who had come to Britain in 1956. Scott was born in Australia in 1929 and was active in British television and film between 1955 and 1981, after which he returned to Australia and continued his career. He featured in two subsequent episodes of The Avengers, both in the filmed era, in Too Many Christmas Trees (1965) and Game (1968).

  • Camera rehearsals for this episode began at 10.00am on Friday 20th January 1961 in Studio 2 at ABC Studios, Broom Road, Teddington Lock, Middlesex. They continued with two one-hour breaks, for lunch at 12.30pm and supper at 6.00pm until 9.00pm that evening. The cast and crew reconvened at 2.30pm the next day, Saturday 21st January 1961, for further camera rehearsals, ending at 6.15pm. After a one-hour break for supper, and a further 45 minutes for camera line-up and make-up, the dress rehearsal commenced at 8.00pm and lasted until 9.30pm. Following another half-hour of camera line-up, the episode was performed and transmitted live, with a planned start and end time of 10.04pm to 11.01pm.

  • Square Root of Evil had a target running time of 52 minutes and 30 seconds. With commercial breaks one of 2 minutes and 5s and and another of 2 minutes and 35 seconds the full duration was planned at 57 minutes and 10 seconds, in common with most episodes produced early in Series 1.

  • The production made use of the following recording equipment: four pedestal cameras, three boom microphones and three slung microphones.

  • On Location... Although this episode went out live, a number of short pre-filmed sequences were played in during the performance. These included an opening teaser scene showing a car on a country lane, surveillance footage of Hooper's gang screened during Steed's briefing, Steed being met by Bloom outside Wandsworth Prison (though the specific building used to represent the location is not known), and Keel arriving by car at Hooper's Garage.

  • The precise nature of the country lane sequence is not known. The surviving camera script says only this: "OPENING TEASER (Car driving along country lane, etc.)". Given the events that follow, two scenarios spring to mind: Steed driving to his briefing, or the dumping of the dead agent Tobert's body. Given that this scene is described as a teaser, which suggests a dramatic event, the dumping of the murdered agent's body seems the more likely possibility.

  • Usually such inserts would be shot on high-resolution 35mm stock, but the camera script for this episode indicates that both 35mm and 16mm film was used. It is possible that the 16mm footage was used for the surveillance film played back during Steed's briefing, since it would not need to be displayed at full-frame size but rather projected on to a screen watched by Steed.

  • Trivia... In a break from the norm for The Avengers, the camera script of this episode indicates that Square Root of Evil opened with a teaser prior to the opening titles, showing a filmed sequence on a country lane. All other episodes of the series, including those from the first year, opened with the title sequence directly after the ABC ident. However, the camera scripts of two other Series 1 episodes The Springers and Double Danger also note the incorporation of teasers, but the surviving Tele-Snaps for these stories reveal that the episodes as transmitted began with title sequences as normal, so it cannot be said with absolute certainty that the same did not happen with Square Root of Evil.

  • Synopses for this episode often describe '5' as a colleague of One-Ten, an assertion which is entirely retrospective as at this point in the series, the character of One-Ten had not appeared or been mentioned. '5', played by Heron Carvic, was the first of Steed's superiors ever to be depicted on screen, though no visual record of this character is known to survive today. Douglas Muir would make his debut as One-Ten later in Series 1, his first confirmed appearance occurring in Diamond Cut Diamond, possibly stepping in because Carvic was unavailable to reprise his role. The plot details of the intervening episodes Nightmare and Crescent Moon are sketchy, and their cast information is quite possibly incomplete, so one cannot rule out the possibility of a reappearance by '5' during these episodes, or an appearance by One-Ten prior to his commonly accepted debut in Diamond Cut Diamond.

  • Episode guides published elsewhere contain some interesting diversions from what actually transpired in the broadcast episode. Many synopses state that '5' has Riordan placed in a safe-house while Steed takes the forger's place. Although that would be a most sensible move, there is no evidence in the camera script that it did indeed happen. The injury to Steed's hand, referred to in several synopses, is not feigned but genuine, although he does use it as a means to make contact with Dr Keel. Contrary to the entry in Dave Rogers' The Complete Avengers (1989), which may have been derived from an unreliable ABC synopsis, Steed does not thrash the Cardinal to within an inch of his life when the villain attacks Lisa, much as the audience might have wished him to. On the contrary, Steed is reluctantly forced to allow the assault to take place. Nor is Bloom the head of the counterfeiting operation rather he is the garage mechanic and Hooper's mysterious boss instead remains unnamed and unseen.

  • Steed adopts an Irish accent while masquerading as the Dublin-born Timothy James Riordan. This is evidenced by Carol's response when Steed telephones the surgery 'in character' as Riordan. At first Carol doesn't recognise his voice, but then she remarks, with reference to a glass of whisky Steed drank earlier in the surgery: "Oh, it's you. Scotch this morning, Irish this afternoon."

  • Carol's duties extend to nursing in this episode. Despite being hired as a receptionist in the previous episode, Brought to Book, she would go on to administer basic healthcare in several subsequent Series 1 episodes, including Hunt the Man Down and Kill the King.

  • In a rare continuity reference, Keel and Steed mention the Rising Sun, Steed's base of operations during Brought to Book. Steed explains that the venue has been closed down by the police. Near the end of the episode, Keel also comments to Steed, "I thought you said my practice wouldn't suffer", another allusion to the preceding episode. Producer Leonard White would eventually clamp down on such references, issuing a production document containing the following directive: "The Avengers is a SERIES, not a SERIAL, and therefore, nothing should be included in scripting, performance or direction, in the nature of 'running gags' (character-building or visual treatment) which are not perfectly acceptable to an audience which has not seen other episodes."

  • The plot element in Square Root of Evil which sees Steed assume the guise of a criminal so that he may infiltrate an organisation who know of the man by reputation and not sight may seem familiar to fans of The Avengers. The later Series 1 episodes, The Springers and Dead of Winter, both feature a similar narrative device, with Keel going undercover as, respectively, Doctors Fenton and Fischer.

  • The events of this episode have an unusually long duration. Approximately three weeks pass between Steed's initial briefing and the resolution of the case. Most of this time elapses between the records room scene and the sequence outside Wandsworth prison, with Steed researching in the intervening time the forgery racket and the man he is to impersonate. A similar two-week break in the narrative occurs in Dead of Winter, to allow Keel to study Dr Fischer's character and history.

  • No episode-specific photographic record of Square Root of Evil is believed to have survived. The story was not 'Tele-Snapped' by John Cura (his invaluable contribution to the understanding of the lost Series 1 commenced with One for the Mortuary) and no rehearsal photographs are known to exist today. A contact sheet, consisting of twelve stills, held by Leonard White are marked by him as "Avengers Episode 3" on the reverse, and appear in the DVD image gallery for this episode. However, the images comprise publicity photographs of Ingrid Hafner and shots of empty sets, rather than scenes from the story itself. The photograph of the actor Alex Scott appearing at the top of this page hails from The Saint episode, The Work of Art (1963), and is included for illustrative purposes only.

  • Bloopers... Not a blooper from the actual episode, but the TV Times listing for it, at the bottom of which it is noted that: "(Carol White appears by permission of Independent Artists)". White was actually in the previous week's instalment, Brought to Book, in which she played Jackie.

  • Stop Press... The Manchester Evening News ran a piece about Patrick Macnee on Saturday 21st January 1961 as part of Max North's Tele-review. The feature focused on Macnee's background, noting his family relationship to David Niven, and that Ludovic Kennedy and Humphrey Lyttleton were amongst his friends at Eton. Macnee recalled his first major film role, with Niven, in The Scarlet Pimpernel, in which he was required to cross the River Loire on horseback: "We spent six months on location, and I seemed to spend most of it in icy water," he commented. Macnee also mentioned his spell on the West End stage, which led to the offer of a part in a television play in Canada, where he stayed for two years. After trips to London and New York, he settled for four years in Hollywood, enjoying the warm climate of Malibu Beach. Unsure of the likelihood of sustained success with The Avengers, he admitted that "I've let it to a friend while I decide whether or not to stay on in England".

  • And Finally... It is open to speculation whether there is any significance in the designation '5'. Does '5' outrank the more prevalent style of numbered codenames, such as One-Ten and One-Twelve? His single digit does suggest a privileged position: if we read One-Ten as '110', for example, then '5' would seem to be much closer to the top of the hierarchy. Alternatively, the 'Ones' could outrank '5'. The Avengers Dossier, a somewhat unreliable reference work from Paul Cornell, Martin Day and Keith Topping, claims that '5' was briefly referred to as 'One-Five' in the episode, but this is not borne out in the camera script. Perhaps the department's numbering system was restructured completely prior to One-Ten's first appearance. On the other hand, these figures might reflect nothing more significant than the building or office numbers in which these characters work. Frankly, they could mean anything, or they could mean nothing at all!

Plotline by Richard McGinlay UK Transmissions by Simon Coward, Alan Hayes and John Tomlinson
Declassified by Richard McGinlay with Alan Hayes

With thanks to Piers Johnson, Dave Matthews, Dave Rogers, Jaz Wiseman and StudioCanal for their kind assistance


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