Doctor Who (1963–1989)
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The Invisible Enemy: Part Two 

The Doctor draws into himself, fighting the voice in his own head that's trying to take over his intelligence.



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Episode complete credited cast:
Brian Grellis ...
Elizabeth Norman ...
Marius' Nurse
Nell Curran ...
Reception Nurse
Nucleus / K9 (voice)
Jim McManus ...
Roderick Smith ...
Kenneth Waller ...


The Doctor and his companion are beset by an alien virus that wants to conquer humankind. The virus swarm possesses the Doctor and now they battle the residents of a local hospital that were all possessed by the swarm. Their only hope lies in a clone of the Doctor. Written by Steph

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Release Date:

8 October 1977 (UK)  »

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Aspect Ratio:

1.33 : 1
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Did You Know?


This episode was watched by 7.3 million viewers on its original transmission. See more »


Doctor Who: Whatever it is I'm suffering from seems to thrive on intellectual activity.
Prof. Marius: Oh, I see. You mean that the harder you think, the more of a grip it seems to take?
Doctor Who: Yeah. Non-thinkng seems to be the only way to shake it off, but I can't stay mindless for eternity, can I?
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User Reviews

What is visible is the huge drop in quality in this story compared to the previous 3 years. Episodes 3 and 4 are just silly.
12 January 2015 | by (South Wales, UK) – See all my reviews

Review of all 4 episodes:

This story is clearly a change in general direction for the series and not a good one. The first part is not bad but is clearly the start of the humour based and rather more childish, lightweight story writing that was forced upon the series by bosses. Part 1 falls into what I would term as the category 'quite fun and enjoyable but not at all outstanding by Doctor Who's very high standards': 7.5/10. Part 2 is in the category of 'OK but a bit disappointing by Doctor Who standards': 7/10. Part 3 then falls quite a lot further down into the category of 'embarrassingly silly and very disappointing by Doctor Who standards': 4.5/10 and Part 4 is almost as bad but not quite as painful as Part 3: 5/10.

The story is a space adventure in which the TARDIS is infiltrated by 'the swarm', an alien intelligence that wishes to spread itself across the universe. The arrival of K-9, the robot dog who becomes The Doctor's companion is notable but the silly and badly carried out idea of cloning and shrinking The Doctor and Leela to fight the virus inside The Doctor's body (an idea re-used to rather better standards in 'Inside the Dalek' in 2014) and the simply awful and embarrassing giant shrimp-like swarm nucleus are real low points. The script and every aspect of Parts 3 and 4 of this story are very poor compared to the series usual expectations. All the more shocking to have this following more than three years of such amazing high quality.

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