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24 September 2014

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The Invisible Enemy

Production Code: 4T

First Transmitted

1 - 01/10/1977 18:15

2 - 08/10/1977 18:05

3 - 15/10/1977 18:10

4 - 22/10/1977 18:10


The TARDIS is infiltrated by the Swarm - a space-borne intelligence that wishes to spread itself across the universe - and the Doctor is infected by its nucleus. The ship then materialises on Titan, one of the moons of Saturn, where the human occupants of a refuelling station have also been taken over.

The Doctor eventually collapses as a result of his infection, but first manages to relay to Leela the coordinates of a local hospital asteroid. At the Bi-Al Foundation, based on the asteroid, Professor Marius clones the two time travellers, miniaturises the clones using the relative dimensional stabiliser from the TARDIS and then injects them into the Doctor's body in the hope that they can find and destroy the nucleus.

The plan backfires as the nucleus escapes from the Doctor in place of the clones and is enlarged to human size. The creature arranges for itself to be taken back to Titan, where breeding tanks have been prepared for it.

The Doctor, now cured of its influence, enlists the help of K9, Professor Marius's dog-shaped robot computer, and sets a booby-trap that results in the breeding tanks being blown up, killing the nucleus. Marius gives K9 to the Doctor as a parting gift.

Episode Endings

The Doctor, infected by the Swarm, aims a gun at Leela's back and prepares to fire.

Marius injects the miniaturised clones of the Doctor and Leela into the Doctor's neck, and they spiral down into his bloodstream.

Marius collects from the Doctor's tear duct what he believes to be the miniaturised clones of the Doctor and Leela and places them into the cloning booth. He operates the controls of the relative dimensional stabiliser to return them to normal size, but instead it is the prawn-like nucleus that appears in the booth.

Marius suggests to the Doctor that he take K9 with him in the TARDIS. The Doctor is reluctant, but Leela is delighted. In the end, K9 decides for himself by trundling in through the open police box doors. The Doctor and Leela follow and, as the ship dematerialises, Marius reflects: 'I only hope he's TARDIS trained.'


The human interior of Richard Fleischer's Fantastic Voyage.

The robots of Silent Running and Star Wars.

Quatermass II (the virus 'spawning' scenes).

The Andromeda Strain.

C.S. Lewis' Out of the Silent Planet (humanity as plague).

James White's 'Sector General' stories (hospital in space with senior consultant and dog).

Late 60s/early 70s medical series like The Expert (with Marius Goring) and Dr Finlay's Casebook (with Andrew Cruikshank).

2001 (design).

Dialogue Triumphs

Lowe, and other characters infected by the Swarm : "Contact has been made!"

The Doctor : "5000 AD! We're still in the time of your ancestors."

Leela : "Ancestors?"

The Doctor : "Yes. That was the year of the great breakout."

Leela : "The great what?"

The Doctor : "Mmm. When your forefathers went leapfrogging across the solar system on their way to the stars. Yes. Asteroid belt's probably teeming with them now. New frontiersmen... pioneers... waiting to spread across the galaxy like a tidal wave... or a disease."

Leela : "Why "disease"? I thought you liked humanity."

The Doctor : "Oh I do, I do. Some of my best friends are humans. When they get together in great numbers other lifeforms sometimes suffer."

Nucleus : "It is the right of every creature across the universe to survive, multiply and perpetuate its species. How else does the predator exist? We are all predators, Doctor. We kill... we devour... to live. Survival is all... You agree?"

The Doctor : "Oh yes, I do, I do. And on your argument, I have a perfect right to dispose of you."

Dialogue Disasters

Nucleus : "The Age of Man is over. The Age of the Virus has begun!"


Leela is learning to write. The white control room is seen for the first time since Pyramids of Mars. The Doctor calls it 'the number two control room' (see The Masque of Mandragora). It has been 'closed for redecoration'. Leela seems to have learned how to operate the TARDIS since she is able to program it to the Bi-Al. Leela tells the receptionist that the Doctor is from Gallifrey which she believes to be in Ireland (see The Hand of Fear). Titan (a moon of Saturn) has the co ordinates quadrant 62, WHI 1212 9990 EX 41. The Centre for Alien Biomorphology (Bi-Al Foundation) is in the asteroid belt on the satellite K4067 (co-ordinates vector 1/9, quadrant 3, 743007).

Attacked by the alien virus, the Doctor lapses into his first self induced cataleptic trance since The Brain of Morbius. The Virus is noetic and therefore only detectable during consciousness, and feeds on 'intellectual activity'. Professor Marius states that the Doctor has 'a symbiotic self renewing cell structure'.

The reflex link in the Doctor's brain meant he could 'tie my brain into the Time Lord intelligentsia'. But he lost the ability 'when they kicked me out!' [A reference to his original departure from Gallifrey (see The Three Doctors for more speculation regarding 'blocks' placed in the Doctor's mind) or to The War Games. This linkage (with the Matrix?) may explain the Doctor's otherwise puzzling comment in Logopolis that he and the Master in many ways have the same mind.]

Marius built K9 not only as a personal data bank, but also to replace the dog he left behind on Earth. K9's attack command (used only in this story) is 'kalaylee'.



The Doctor's Doctorate


Titan and the Bi-Al Foundation, c. 5000.

Future History

The story takes place 'at the time of the Great Break Out' of 5000 AD, when mankind 'went leapfrogging across the galaxy like a tidal wave, or a disease'. [Their numbers were doubtless swollen by people trying to escape from Magnus Greel: see The Talons of Weng Chiang.]

K9 states the first successful cloning experiments were carried out in the year 3922 adding 'the Kilbracken holograph cloning technique replicates from a single cell a short lived copy. Efficiency of individualisation not completely guaranteed.' The longest successful clone lasted for 10 minutes 55 seconds. Marius notes the Kilbracken technique is simple but 'it's a circus trick, it has no practical value'.


The traditional TARDIS control room set returns, albeit slightly redesigned by Barry Newbery.


Professor Marius is said to be an expert in extra terrestrial pathological endomorphisms [alien diseases caused by a geological process of rock metamorphosis?!?]


As pointed out in a letter to Radio Times the clones of the Doctor and Leela should have been naked when they are created.

Leela's antibodies are a time paradox: she is descended from people who left Earth after this story, and by being present in 5000 AD she gives humanity the antibodies she has always possessed (as a result of her trip to 5000 AD!)

Why does the Titan relief crew kill the men they are relieving rather than just infect them?

The TARDIS' dimensional stabilizer just so happens to fit into Marius' equipment (cf. Full Circle)

There are guns without triggers or holes in the barrel.

Marius' operating room is clearly a TV studio (it has no roof).

The first shot of the Bi-Al Foundation shows it with the damage later caused by the shuttle crash.

When K9 blasts a chunk out of the wall, it's obviously a pre-cut segment.

If K9 is Marius' 'best friend', as he says, why is he so content to part with the dog?

Cast & Crew


The Doctor - Tom Baker

Leela - Louise Jameson

Voice of K9 - John Leeson

Crewman - Anthony Rowlands

Cruikshank - Roderick Smith

Hedges - Kenneth Waller

Lowe - Michael Sheard

Marius' Nurse - Elizabeth Norman

Medic - Pat Gorman

Meeker - Edmund Pegge

Nucleus - John Scott Martin

Nucleus Voice - John Leeson On Parts Two to Four John Leeson was credited as 'Nucleus and K9 Voice'

Opthalmologist - Jim McManus

Parsons - Roy Herrick

Professor Marius - Frederick Jaeger

Reception Nurse - Neil Curran

Safran - Brian Grellis

Silvey - Jay Neill


Director - Derrick Goodwin

Assistant Floor Manager - Tony Garrick

Assistant Floor Manager - Christabel Albery

Costumes - Raymond Hughes

Designer - Barry Newbery

Film Cameraman - Nick Allder

Film Editor - Glenn Hyde

Incidental Music - Dudley Simpson

Make-Up - Maureen Winslade

Producer - Graham Williams

Production Assistant - Norman Stewart

Production Unit Manager - John Nathan-Turner

Script Editor - Robert Holmes

Special Sounds - Dick Mills

Studio Lighting - Brian Clemett

Studio Sound - Michael McCarthy

Title Music - Ron Grainer and the BBC Radiophonic Workshop, arranged by Delia Derbyshire

Visual Effects - Tony Harding

Visual Effects - Ian Scoones

Writer - Bob Baker

Writer - Dave Martin

Bottom Line - from The Discontinuity Guide

'Contact has been made...' An ambitious project which has the look of a grand folly due to budget constraints and the tongue-in-cheek script. Great model work is dwarfed by the weight of the story's faults. K9 makes a quite impressive debut, though, as with many aspects of The Invisible Enemy, the ideas are better than the realisation.

Analysis - from Doctor Who, the Television Companion

After the promising start made in Horror of Fang Rock, many viewers would no doubt have entertained hopes that the quality of the fifteenth season would match that of the fourteenth. Such hopes would have been soundly dashed by The Invisible Enemy, which is one of the weakest stories of the fourth Doctor's era. Reviewers over the years have struggled to find a good word to say about it. 'The basic idea behind this story of an enemy invading from within the human nervous system was an interesting and novel one,' conceded Howard D Langford in TARDIS Volume 3 Number 3, dated May/June 1978. 'However, having said this, the story was handled badly. The action seemed to be at too fast a rate - I preferred the slower tempo of Horror of Fang Rock. The introduction of K9 was a disaster which led to inevitable tedious fighting. If we want lasers blasting we can watch Star Wars, not Doctor Who... Finally, the blowing up of the nucleus was the sort of action that the Doctor deplored in Doctor Who and the Silurians, yet here we find him resorting to destruction à la Leela. He was supposed to be educating her, not vice versa!'

A particularly notable aspect of this story is its heavy reliance on visual effects. The model shots are the most extensive and ambitious to be featured in the series thus far, and are undoubtedly one of the highlights of the production. Even they have come in for criticism, however. 'It was the visual effects that spoiled the show,' argued Kevin Davies in Quark 1, dated November 1977. 'The spaceship models were excellent... but were reduced to "things on strings" once on screen. The Titan base was straight from Space: 1999, and its eventual destruction was awful. Blaster rays issued from anywhere but the gun nozzles, CSO screens looked unconvincing, as usual, and K9 fired at a pre-cracked wall in order to make a barrier small enough for a puppy K9 to jump over.'

In fairness to designer Barry Newbery, whose characteristically excellent work is the other highlight of the production, it should be pointed out that the pre-cracking of the wall fired at by K9 was successfully disguised when the scene in question was first recorded; unfortunately director Derrick Goodwin called for retakes and the broken section of the wall had to be replaced with insufficient time available for the join to be repaired.

The scenes in which the clones (or rather pseudo-clones, complete with clothes, produced by something referred to as the 'Kilbracken technique') make their way through the Doctor's body are highly reminiscent of the 1966 Twentieth Century Fox production Fantastic Voyage. They work nowhere near as well, however, owing partly to the fact that, whereas in the film the voyagers had a ship with its own atmosphere, here the clones are moving about as if they are in the open air, and partly to the fact that on Doctor Who's relatively small budget the effects that could be achieved were visibly inferior. These scenes are nevertheless some of the more successful ones in the story - although the appearance of the human-sized version of the nucleus of the Swarm at the end of Part Three is very much a let-down, as Keith Miller pointed out in Doctor Who Digest Number 8, dated April 1978:

'I really liked the scene when the Doctor "short circuited" his liver to save Leela from the balloon-type antibodies. The chasm between the brain and the mind left a lot to be desired, but who knows, perhaps such a thing does exist... The meeting between the Doctor... [and the nucleus] was very good, expertly written and acted. However, it isn't long before the nucleus escapes through the Doctor's tear duct and enlarges into one of the funniest Doctor Who monsters I've seen in a long time...

'The remaining struggle to get back to the hive and its inevitable destruction [were] quite well done, but all believability was gone because of the farcical monster. Pity. I had enjoyed the other three episodes.'

Writers Bob Baker and Dave Martin seem to have developed a liking for giving their characters 'catchphrases'. In The Hand of Fear it was 'Eldrad must live!', this time it is 'Contact has been made!' (and later in the season in Underworld it will be 'The quest is the quest!'). Unfortunately this is one of the few memorable aspects of the scripts, which generally consist of clichßd and undemanding action-adventure material. We will leave the final word to the particularly unimpressed John Peel, who wrote in TARDIS Volume 2 Number 8 in 1977: 'The production team seem convinced that Doctor Who is really a kid's show, and have proved it so admirably with the latest serial. Despite superficial glitter, good miniatures and Frederick Jaeger's superb acting [as Professor Marius] (didn't seem a bit like Sorenson [in Planet of Evil], did he?), The Invisible Enemy failed miserably as entertainment... The Doctor now has a mechanical pet to go with his savage. With stories like this one and Horror of Fang Rock, why not a new time slot as well? Straight after Watch with Mother. The [series] is going to the dogs!'

< Horror of Fang RockFourth DoctorImage of the Fendahl >

This episode guide is made up of the text of The Discontinuity Guide by Paul Cornell, Martin Day and Keith Topping, and Doctor Who: The Television Companion by David J. Howe and Stephen James Walker.

The Discontinuity Guide © Paul Cornell, Martin Day and Keith Topping 1995.
Doctor Who: The Television Companion © David J Howe and Stephen James Walker 1998, 2003.

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