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The Invisible Enemy: Misc


Dr Who

Up to date as of January 31, 2010

From TARDIS Index File, the free Doctor Who reference.

"The age of Man is over, Doctor. The age of the virus has begun"
The Invisible Enemy
Series: Doctor Who - TV Stories
Season Number: Season 15
Story Number: 93
Doctor: Fourth Doctor
Enemy: The Swarm
Writer: Bob Baker and
Dave Martin
Director: Derrick Goodwin
Broadcast: 1st October - 22nd October 1977
Format: 4 25-minute Episodes
Previous Story: Horror of Fang Rock
Following Story: Image of the Fendahl



A rocket with three men are near complete their mission to Titan Base until a course change puts the rocket in the path of a strange cloud in space. By the time they have arrived, they have changed and serve a sentient virus which threatens the galaxy. When the TARDIS picks up an emergency message, it flies into the cloud, infecting the Doctor himself. To save himself and others, the Doctor must undertake a dangerous journey.


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.




  • K9 states the first successful cloning experiments were carried out in the year 3922. He adds that "the Kilbracken holograph cloning technique replicates from a single cell a short lived copy. Efficiency of individualisation not completely guaranteed."
  • Professor Marius is said to be an expert in extra terrestrial pathological endomorphisms.
  • 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.
  • Marius presumes that the Doctor is a spacenik.

Story Notes

  • This story had the working titles; The Invader Within, The Enemy Within and The Invisible Invader.
  • This story was listed on the 1970s sound effects LP as "The Enemy Within" which would go on to become the second-hand title given to the 1996 television movie.
  • This is the story which introduced K-9.
  • This story also re-introduces the 'old' white console room (though slightly redesigned by Barry Newbery) rather than the 'wooden' secondary console room which debuted in The Masque of Mandragora.
  • Leela is left-handed, or at least writes with her left hand. Actress Louise Jameson is right-handed, but chose to make Leela a left-handed writer in order to increase her awkwardness at this task.


  • Part 1 - 8.6 million viewers
  • Part 2 - 7.3 million viewers
  • Part 3 - 7.5 million viewers
  • Part 4 - 8.3 million viewers


to be added

Filming Locations

Discontinuity, Plot Holes, Errors

  • When the TARDIS first arrives on Titan, in the background you can see one of the relief ship crew still helmeted.
  • Why when the infected crew members arrive on Titan don't they infect the base personnel instead of killing them? The crew member's infection is still in its early stages and is not yet contagious.
  • The cloning of the Doctor and Leela seems to have also cloned their clothes. (No doubt due to 51st century technological advances in regard to modesty).
  • Several times during the episode, the signs for the "Isolation Ward" are spelled "Isolayshun." (This is not an error, but an intentional aspect of the design to show a progression of the language at this point in history to phonetic spelling - i.e. spelling a word as it sounds. There are other such spellings, not only with the Isolation Ward but in the various other locations in which this story is set. )
  • The interior of the Doctor's brain seems strangely lacking in fluid and other mucas that would drown the miniaturised Doctor & Leela. Also why is there a 'screen' with pictures of cogs and pillars floating across it? The Doctor's brain is that of a Time Lord, therefore there is no reason to believe its physiology should in any way be in keeping with the principles of human neurobiology. (Specific mention is also made that the miniaturised clones are not massive enough to break the fluid tension, implying that fluid is present but not discernible.)
  • 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!)
  • The TARDIS' dimensional stabilizer just so happens to fit into Marius' equipment
  • 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?
  • When the shuttle lands on Titan, the Captain flips down all the switches on the control. But he misses one
  • The surface of Titan – rocky with a clear view of Saturn – is inconsistent with what was known about Titan at the time the episode was made. It should be gaseous with an opaque orange sky.
  • Lowe's "frozen" makeup changes between when he emerges from the freezer and when Leela brings him a cup of coffee.
  • The knife that Leela kills Meeker with is very obviously loosely sewn to his clothes. Notice how it wobbles back and forth after he falls.
  • Leela and the Doctor use different console levers to operate the TARDIS doors.
  • Why doesn't Lowe simply shoot Leela the second her back is turned? Moreover, why does he take them to get medical help? It's made clear that the virus has everything it needs on Titan.
  • The proportions of the shrinking Doctor and Leela clones is way off. At the point where they are two feet tall, they are still visible from above the waist (the foot tall door sill blocks everything below the waist). Their legs would have to be about 6” tall relatively to their 1-1/2’ bodies, torsos, and heads.
  • When Marius injects the cloned Doctor and Leela into the real Doctor, the syringe is obviously just filled with air. But the next shot shows them in liquid.
  • In the very first scene, as the Doctor collapses to the ground, a person can be seen moving in the back of the set.
  • Why does Marius clone (and presumably re-infect) Lowe before injecting him? The Doctor needed to be cloned to go into his own mind, but Lowe doesn't.
  • After the Doctor and Leela's clones fade, the camera pans to show Leela's knife. But since the knife was created in the cloning process, it should have faded out with Leela, the Doctor and their other personal items.
  •  The Doctor's clone is free of the virus, so why is Lowe's clone infected? Perhaps they infected him after cloning, in which case, why is Lowe cloned at all?
  • The readout strip dangling from K-9's mouth shortens between shooting the infected crewman and shooting Leela.
  • When K-9 shoots the infected man in episode three, there is a readout strip coming out of his mouth for some reason.
  •  When K-9 shoots one of the infected men, the blast beam appears to come out of his eyes, then moves down to his snout as the camera moves.
  • The countdown clock in Marius's lab speeds up and slows down as needed for the plot.
  • When the Doctor is congratulating himself on blowing up the Swarm, the shadow of a boom mike can be seen.



DVD, Video and Other Releases

DVD release

  • This story was on DVD release on 16 June, 2008 in a K-9 Tales Box Set. It was released in the Box Set alongside K-9 and Company.
  • Early versions of the box set feature a fault on The Invisible Enemy disc. A scene from half way through episode 3 is skipped and appears after the closing credits. 2 entertain is aware of the problem but have decided to go on with the release as planned. Though they are trying to fix the problem for later copies of the DVD box set.



Main article: Doctor Who and the Invisible Enemy

See also

  • NA: Timewyrm: Revelation (journey into the Doctor's mind)

Stories involving shrinking

External Links

  • BBC Episode Guide for The Invisible Enemy
  • Doctor Who Reference Guide: Detailed Synopsis - The Invisible Enemy
  • A Brief History of Time (Travel) Guide to The Invisible Enemy
Season 15
Horror of Fang Rock  • The Invisible Enemy  • Image of the Fendahl  • The Sun Makers  • Underworld  • The Invasion of Time

This article uses material from the "The Invisible Enemy" article on the Dr Who wiki at Wikia and is licensed under the Creative Commons Attribution-Share Alike License.

ST Expanded

Up to date as of February 07, 2010

The Star Trek Expanded Universe Database is for fanon and related content. See for the canon Star Trek wiki.

This article has a
real-world perspective.

"The Invisible Enemy" was the twenty-eighth episode of Star Trek: Phoenix-X, and the third episode of the second season.


Kayl meets a new friend over the telepathic-web. Little does she realize this "friend"'s despicable intentions. Meanwhile, the Phoenix-X is sent to the Morcas planet, in the Lorkas sector, to uncover its sick and twisted mystery.

Background information

External links

  • Episode 28 - "The Invisible Enemy" on the Phoenix-X message boards
  • Episode 28 - "The Invisible Enemy" on the Phoenix-X website

This article uses material from the "The Invisible Enemy" article on the ST Expanded wiki at Wikia and is licensed under the Creative Commons Attribution-Share Alike License.


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