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Relative Dimensions was the seventh story in the fourth series of the Eighth Doctor Adventures, produced by Big Finish Productions. It was written by Marc Platt and featured Paul McGann as the Eighth Doctor and Sheridan Smith as Lucie Miller.

It served as Big Finish's 2010 Christmas special release and featured Susan and Alex Campbell (portrayed by Carole Ann Ford and Jake McGann respectively). In this adventure, the Doctor intended to spend Christmas with Susan and Alex, his great-grandson whom he had met for the first time in the audio story An Earthly Child. But a present he got for Susan a long time ago, in the audio story Quinnis, may jeopardise the perfect Christmas he had promised Lucie to make it up to her for their previous disastrous Christmas described in Death in Blackpool. This story was the only story on television or audio where the Doctor celebrated Christmas with his family.

Publisher's summary

Christmas is a time for family, they say — which is why the Doctor has invited his grand-daughter Susan and great-grandson Alex for Christmas dinner in his time and space machine. But who, or what, is the spectre at their yuletide feast?

Venturing deep into the dark heart of the TARDIS, Susan uncovers her past, Alex is told his future — and the Doctor finds himself caught in a deadly dangerous present!


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  • At Lucie's suggestion, she and the Doctor do their Christmas shopping during the subsequent January sales. He is able to pay for the gifts using his previously untouched UNIT salary, which has accrued a great deal of interest over the years.
  • The TARDIS' Christmas tree is a Norwegian spruce, which Lucie picked out herself. They intend to return it once Christmas is over.
  • For Christmas, both Susan and Lucie bought socks for the Doctor while the Doctor intended to give Lucie socks as well as a TARDIS key with a musical ringtone.
  • Susan builds a snowman version of the First Doctor with a carrot for a nose and two brussels sprouts for his eyes.
  • The Doctor wants to watch Queen Elizabeth II's Christmas Speech from 25 December 1953 using the Time-Space Visualiser.

Historical figures

  • The Doctor tells Susan, Lucie and Alex that Leonardo da Vinci begged him to take him to Bethlehem in order to witness the birth of Jesus Christ as he wanted his Adoration of the Magi to be as accurate as possible. The Doctor was able to work out the date by reference to the census records in Rome. The two of them checked all of the inns in Bethlehem and eventually found one with a stable attached. However, Leonardo refuses to look into the stable for fear of disappointment. When the Doctor mentioned his "mate Leonardo," Lucie erroneously believed that he was referring to the American film actor Leonardo DiCaprio.


  • Alex's full name is Alexander David Campbell. He is 18 years old.
  • Although Alex is the Doctor's great-grandson, he nevertheless refers to the Doctor as "Granddad."
  • Alex is studying the history of European architecture in London.
  • Alex is not telepathic and cannot regenerate. The Doctor analyses his DNA and discovers that his Gallifreyan genes constitute only 7% of his genome.


  • During their travels together, the First Doctor and Susan travelled to the planet Ambrosia, where everything smelled of spice apart from their sovereign.


  • The TARDIS contains a colony of bats known as fledershrews.
  • The Doctor, Lucie, Susan and Alex are attacked in the TARDIS library by an eight foot alien fish with "fearsome spines and quills" and an armoured, electric carapace. It is able to swim through the air and travel between different dimensions as well as through time.
  • The air fish is known as a Blitzen fish or Resurrection fish as it is able to survive long periods of hibernation. It is used for hunting in the fourth universe. The longest known specimen is 14.7 metres. They are native to the Aurora Gloriousia in the fourth universe.


  • The Doctor alters the TARDIS' internal dimensions to recreate Susan's old room, which had been held in storage in the TARDIS holding ring. The Doctor determines that his downloading of the room resurrected the air fish, which travels back in time to ensure that it was released from Susan's room. The Doctor is electrocuted by the energy discharge produced by the collision of the two versions of the fish. He had hoped that the present and future versions of the fish would cancel each other out due to the Blinovitch Limitation Effect.
  • The TARDIS holding ring contains the stored rooms of all of the Doctor's previous companions, including Ian Chesterton, Barbara Wright, Vicki Pallister, Steven Taylor, Dodo Chaplet, Polly Wright, Ben Jackson, Jamie McCrimmon, Victoria Waterfield and Tamsin Drew. He has also created one for Alex. However, he eventually decides to delete all but one of these.
  • The Doctor intends to give the TARDIS to Alex at some point, though only after he has travelled with him. However, Alex decides to go on a grand tour of Europe with Lucie instead.

Time Lords

  • Alex was previously unaware that Time Lords have two hearts. Susan does not answer when he asks if she also has two hearts.



External links