Castrovalva
The Doctor is unstable after regenerating, leaving the operation of the TARDIS to his companions, Nyssa and Tegan.  The Doctor is unaware that the Master has captured Adric and is using him to lay a series of traps to bring about the Doctor's demise.  Narrowly escaping one trap which propelled the TARDIS back towards event one, or the "Big Bang", Tegan lands the TARDIS near Castrovalva, which according to the index file, is so peaceful it can premote healing of the regeneration process.  This too is a trap set by the Master.  The TARDIS has no Index file and Castrovalva is a paradoxial dimensional trap.  The Doctor regains his senses and defeats the Master and Adric is set free.

I enjoyed this stoy quite a bit.  It showed many creative techniques including the paradoxal Castrovalva.  One rememorable seen is shortly after the Doctor's regeneration.  He wanders throught the halls impersionating his previous incarnations.  However, the unraveling of Tom Baker's scarf nearly made me burn the damned thing.  Bad move Nathan~Turner.
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