Season 15, Episode 2 | 4 parts | First broadcast: 1–22 October 1977 | Writer: Bob Baker and Dave Martin | Director: Derrick Goodwin
Cast
- Tom Baker as the Doctor
- Louise Jameson as Leela
- John Leeson as the voice of K9
- Frederick Jaeger as Professor Marius
Summary
Infected by a swift-spreading intelligent virus during a space voyage, the Doctor finds his mind under threat from the Nucleus of the Swarm, an alien entity intent on using his body and knowledge to spread itself across the galaxy. To fight back, a miniaturised Doctor and Leela are sent inside his own body to confront the infection directly, while on a nearby asteroid base a brilliant scientist’s newly built robotic dog proves an unexpected ally in the battle against the Nucleus’s escalating plans.
Interesting Facts
- This serial introduces K9, the robotic dog companion who would become one of the most popular and enduring characters of the classic series.
- The “miniaturised journey through the body” concept was a deliberate homage to the science-fiction film Fantastic Voyage.
- The Nucleus of the Swarm’s final prawn-like enlarged form was widely mocked by fans and critics as one of the era’s less convincing creature effects.
- John Leeson’s voice work as K9 began here and would continue, on and off, across decades of both the classic series and its spin-offs.
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