The Doctor’s latest regeneration has proven more unstable than his previous ones. His two assistants, Tegan and Nyssa, help him recuperate on the tranquil planet of Castrovalva.

Adric has been captured by The Master, who is taking advantage of the Doctor’s weakened state to ensnare him in an elaborate trap whose recursive nature threatens to destroy his mind.

As The Doctor begins to recover he realises that The Master’s trap for Adric is even more intricate than he could have imagined and that he will stop at nothing to gain his revenge over The Doctor.

Episode guide


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coming soon


  • Peter Davisons debut story
  • Final part of the Master trilogy
  • Mergrave offers a tonic drink to The Doctor, who recognises Valeriana officinalis centiculare europea and a hint of rosemary among its ingredients.
  • The Masteruses a Hadron web, which is powered by Adric, to power his creation, Castrovalva.
  • As they move through The Doctor’s TARDIS, Nyssa and Tegan discuss the sensation that they are heading downward, despite the absence of stairs or obvious slant of the floors.
  • Seventeen thousand tons of thrust, corresponding to a quarter of the mass of the TARDIS, are jettisoned to escape the Event One.

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