• title card: SQUARE ROOT OF EVIL superimposed on a reel tape recorder (recreated by Richard McGinlay)

Series 1 - Episode 3
Square Root Of Evil

by Richard Harris

Production completed: 21 January 1961. First transmission: 21 January 1961

TV Times summary

The corpse and the “Cardinal” turn Steed into someone whom the lovely Lisa may prefer dead

The following episode summary is written from the original scripts as this episode is now lost. There may have been changes made during filming.


A car speeds along a deserted country lane in blackest night, as it passes by, a door opens and a man's body is flung out, tumbling into the ditch at the side of the road.

Act I

Steed's boss, "5" (Heron Carvic) informs him that another agent, Tobert, was found dead while investigating a forgery racket run by Charles Hooper and Jimmy Bishop, AKA "The Cardinal". 5 orders Steed to impersonate Timothy Riordan, an Irish master forger that Hooper has recruited; Riordan is due to be released from prison in three weeks. John Steed (Patrick Macnee) is pensive about being 6", taller than Riordan, but 5 believes none of the gang have ever met him. 5's secretary (Cynthia Bizeray) leads Steed to the records room and, fending off Steed's sexual advances, plays a film of Hooper's gang so Steed can identify them.

Steed is picked up outside Wandsworth Prison by Steve Bloom (John Woodvine) and taken to Hooper's print shop to meet the gang. At the print shop, Warren (Vic Wise) has just finished a stack of £18,000 worth of forged notes when Steed and Bloom arrive. Hooper (George Murcell) tells Steed that their printing plates are wearing out and he wants him to make new ones. Steed claims he's going straight and isn't interested - until Hooper shows him one of their notes and offers £10,000. The Cardinal (Alex Scott) enters, wearing his fedora pulled down to obscure his face.

CARDINAL: So you’re Riordan.
STEED: Who’s the poor man’s Al Capone?
HOOPER: This is Jimmy Bishop. He’s my righthand man.
CARDINAL: You’d be wise to remember that Riordan.
STEED: Somehow I can’t see you letting me forget.

Steed has annoyed The Cardinal and tests Steed's bona fides with regard to knowing the prison he supposedly just left. Steed passes the test so they show Steed the set-up, and Hooper confesses they haven't distributed any forgeries yet. Steed finally agrees that he's in on it and is startled when The Cardinal says he has a surprise for him - one of his old girlfriends, Lisa, is outside in the car! Lisa (Delphi Lawrence) is brought in and she greets him effusively. Steed kisses her deeply then, knowing it's a trap, turns to The Cardinal and tells him to stop playing games, he's never seen Lisa before in his life!

Act II

Warren is at his flat, discussing a post office hold-up with Steed and reveals that he used to run a legitimate wedding stationery business. Steed asks why he doesn't live above Hooper's garage and learns they were all kicked out when The Cardinal turned up; Warren is wary of The Cardinal because he carries a gun; he's a bit too hard core gangster for him. Steed departs, claiming he's going to place a bet on the dogs but actually rings 5, informing him that he's infiltrated the gang and The Cardinal tried the phony girlfriend stunt, using his wife. Steed plans to check out the safe that night as The Cardinal and Hooper will be away collecting the next load of paper.

Steed arrives at the garage and enters to search the safe, unaware that someone was in one of the cars and is now silently following him. As he leaves, the lights come on, revealing Lisa who confronts him. She tells him she might not tell The Cardinal what he's doing, but she knows he's not Riordan.

STEED: Why didn’t you say anything then?
LISA: Because ... because I knew what it would mean. I met The Cardinal two years ago. He talked big and threw money around and I was impressed enough to marry him. When we moved in here with Hooper, I knew he was in some sort of racket but ... it didn’t matter. But now he’s changed. He’s vicious - suspicious of everybody. And he’s started carrying a gun.

Steed warns her that he has "enough evidence to make things red-hot for all of you".

Hooper and The Cardinal return and Steed goes to spy on them. He overhears Jimmy saying that he doesn't like the gang getting larger, and wants Hooper to tell him more about the operation. Steed watches them stacking the paper but then a truck loaded with paper runs into the bench where he's hiding, injuring his hand. After escaping quietly, holding his hand to lessen the pain, he tells Lisa to go back to her room and say nothing. However, realising Steed is about to be caught as Jimmy returns, she deliberately makes a noise, drawing Jimmy's attention. He cruelly hits her for sticking her nose into things that don't involve her. Hooper protests, and Steed has to fight the urge to intervene.


Steed visits Dr David Keel (Ian Hendry) to get his cut hand fixed, asking Carol Wilson (Ingrid Hafner) for a large Scotch to take away the pain. He's worried about Lisa, if she hadn't shown herself when she did, Keel would be dealing with a corpse instead of a cut hand. Steed calls 5 and tells him Dr Keel has been told about the case in case they need him, and he's dropped off some film at the chemist. Hanging up, Steed gives Keel 5's number - WHItehall 0011 - as Carol prepares an antibiotic injection for his hand.

Lisa learns that Jimmy is suspicious of Steed and had heard Steed was seen with a plain-clothes copper the previous night but Lisa persuades him Riordan wouldn't throw away the money for those who put him inside. Hooper arrives and calls the gang into his office, angrily telling Jimmy to get out of his chair. He announces the boss will collect the money that night. Bloom is concerned as they've only done half the job and Hooper explains the boss planned it that way to stop loose talk; the job is complete. Steed complains they haven't used him yet and won't get any money but Hooper promises him half they offered, or the full amount if he stays on for the next job. He then orders them all to crate up the presses as they're moving the whole operation.

Steed goes to call Keel, saying he needs both his hands, but The Cardinal doesn't want to let him, saying as soon as they talk about moving he wants to make a phone call. Hooper agrees but finally decides to call Dr Keel on his behalf. When Hooper hears he has rung a real doctor he lets Steed take the phone.

STEED: (DISTORT) My name’s Riordan ... it’s about an appointment I have with the doctor ...
CAROL: Mr. Riordan? I don’t ..
STEED: (DISTORT) I’m a new patient. I came for the first time this morning. Mr. Steed recommended me.
CAROL: [LAUGHS] Oh, it’s you. Scotch this morning, Irish this afternoon.2

Steed manages to pass on a warning to Keel by saying his "firm won't let him go" and they will "be working very late". Dr Keel immediately calls 5 to deliver the message. 5 doesn't want to make a move as they're after the man behind Hooper so he asks Keel to visit the garage to see what's going on while he organises a discreet police cordon.

The gang are packing up when the door bell rings, making them jumpy. It's Dr Keel, who Hooper leads into his office. He goes to give Steed another injection but The Cardinal doesn't buy it and orders them down to the print room at gun point. He tells Hooper he never trusted Riordan and now the doctor's seen too much there's only one thing to do. Jimmy says to Steed, "If you're one of us - kill him". Steed refuses and points the gun at Jimmy instead. The Cardinal sneers at him and shows the cartridges in his hand, the gun is unloaded. He launches himself at Steed with a roar and they fight, Keel and Lisa siding with Steed and Warren and Hooper with The Cardinal, employing printing equipment as weapons. With the gang rounded up and Lisa allowed to go free,3 Steed muses that they can catch the real "Number 1" by replacing the gang with some of their own boys.

1. This film insert seems to have been reused in Toy Trap when Lennie is killed.
2. Carol's joke is in reference to Steed asking her for a large Scotch to take away the pain when he visited earlier, and the Irish accent he's using when impersonating Riordan.
3. The details about who joined the fight and Lisa being allowed to go free come from The Complete Avengers by Dave Rogers (Boxtree/St. Martin's Press First U.S. Edition paperback, 1995, p. 19) but are not in the camera script, other than Steed telling Jackie Warren the party is over at the end.


Legend:CreditedCredited but not listed in TV TimesUncredited
John Steed Patrick Macnee regular007
"Five" ® Heron Carvic Police SurgeonDoctor Who
The Secretary ® Cynthia Bizeray regular
Steve Bloom ® John Woodvine regularDoctor WhoDangermanThe ChampionsThe Saint
Charles Hooper ® George Murcell regularDangerman007The ProfessionalsThe SaintJason KingRandall and HopkirkThe Champions
Jackie Warren ® Vic Wise regular
The Cardinal (Jimmy Bishop) ® Alex Scott regularDangermanThe SaintSpace 1999Randall and HopkirkDepartment SJason KingAdam Adamant
Lisa ® Delphi Lawrence DangermanThe Saint
Carol Wilson Ingrid Hafner regularPolice Surgeon
Dr David Keel Ian Hendry regularDangermanPolice SurgeonThe SaintThe Sweeney
Tobert unknown (voice only)

* Michael Robbins was originally cast to play Bloom.

Images from other sources: Delphi Lawrence from a publicity still, Alex Scott from "Ghost Squad": "Ticket for Blackmail", John Woodvine from "The Man of the World": "The Bandit", Cynthia Bizeray from a publicity still, Heron Carvic from a publicity still, George Murcell from "The Four Just Men": "The Godfather", Vic Wise from "Kill Me Tomorrow".


Legend:CreditedCredited but not listed in TV TimesUncredited
Teleplay by Richard Harris regularThe SaintAdam AdamantPolice SurgeonThe Sweeney
from a story by John Bryce regular
"The Avengers" Theme composed and played by Johnny Dankworth regular
Designed by Patrick Downing regular
Producer Leonard White regularCallanPolice Surgeon
Directed by Don Leaver regularCallanPolice Surgeon
Story Editor John Bryce regular
Production Assistant Barbara Forster regular
Floor Manager Geoff Smith regular
Stage Manager Nansi Davies regular
Call Boy unknown
Lighting Director Peter Kew regular
Operational Supervisor Peter Wayne regular
Senior Cameraman Michael Baldock regular (listed as Mike Baldock)
Sound Supervisor Peter Cazaly regular
Vision Mixer Del Randall regular
An ABC Network Production

Production and transmission details

Studio details: Teddington Two
Production No. 3367
Tape No. VTR/ABC/1089 (Rec. off T/X)
Transmission: 21st January 1961, 10.00-11.00 p.m.


Friday, 20th January 1961
Camera Rehearsal10.00 - 12.30
Lunch Break12.30 - 13.30
Camera Rehearsal13.30 - 18.00
Supper Break18.00 - 19.00
Camera Rehearsal19.00 - 21.00
Saturday, 21st January 1961
Camera Rehearsal14.30 - 18.15
Supper Break18.15 - 19.15
Normal scan, line-up and Make-up19.15 - 20.00
Dress rehearsal20.00 - 21.30
Line-up21.30 - 22.00
TRANSMISSION22.00 - 23.00


Cameras: 4 Pedestals
Sound: 3 booms, slung mics
Telecine: ABC symbol, 35mm & 16mm mute inserts, Slides

Total running time: 57.10 = Play portion: 52.30 + 2 commercial breaks: 2.05 and 2.35

TV Times listing

TV times listing for January 21 1961, showing The Avengers in the 10pm timeslot (January 13 1961 Northern edition), incorrectly referencing Carol White

Teleplay by Richard Harris
Also starring

Cast in order of appearance:

John Steed Patrick Macnee
“5” Heron Carvic
Secretary Cynthia Bizeray
Bloom Michael Robbins
Hooper George Murcell
Warren Vic Wise
The Cardinal Alex Scott
Lisa Delphi Lawrence
Carol Wilson Ingrid Hafner
Dr David Keel Ian Hendry

“The Avengers” theme composed and
played by Johnny Dankworth
Designed by Patrick Downing
Directed by DON LEAVER

The corpse and the “Cardinal” turn Steed
into someone whom the lovely Lisa may
prefer dead

(Carol White appears by permission of
Independent Artists)


The cast list above has Michael Robbins playing Bloom but he was unavailable when recording took place and John Woodvine played the part. The TV Times listing also mentions permission for Carol White to appear, which should have been for the previous episode, see the notes below.

Regional broadcasts

ITV BroadcasterDateTime
ABC Midlands21/01/196110.00pm
ABC North21/01/196110.00pm
Anglia Television--
Southern Television--
Tyne Tees Television--
Television Wales & West--
Ulster Television--
Westward Television--
Scottish Television--
Border Television--
Grampian Television--

Episode availability

  • Video - none
  • Audio - reconstruction in The Lost Episodes vol. 1, by Big Finish
  • Script - clean archive copies of the original camera and rehearsal script, from a private collection and distributed by Studio Canal
  • Publicity Stills - none
  • Tele-Snaps - none


  1. This is the third episode in a row that features a shadowy, unknown boss behind the gang at the centre of the action. This boss presumably gets away again at the end of the episode but it's unclear as the episode ends with Steed musing that they might be able to capture him.
    This seems to be a vestige of a possible early writers' directive to have a Moriarty figure in each episode and it may have been dropped after this episode.
  2. The camera script notes that the episode is to be recorded off transmission.

  3. A memo dated 30 March 1962 proposed a replay season for the nine episodes not broadcast by ATV and Anglia and also the first two episodes, which had been seen on ATV but not Anglia. This proves that all live episodes had been recorded any may yet be out there somewhere.
    This episode was proposed to be run fourth, slipping down the order behind other episodes but still well regarded even though it was in the second category of viewer ratings.
  4. The TV Times accidentally printed the notice "(Carol White appears by permission of Independent Artists)" against this episode's listing; it should have been printed a week earlier for Brought To Book.
  5. This is one of three episodes in series 1 which had a pre-titles teaser in the script - Square Root of Evil, The Springers and Double Danger - but none of them are recorded in Tele-Snaps or production stills so there's no proof that they were broadcast in that manner.

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