They met a few minutes later in the console room, Tegan having dressed also.  The Doctor stood by the console for a few minutes, listening to the details of Tegan's story, tapping his lips with a finger as if waiting for inspiration.  'I see,' he concluded.  'Now help me think, Tegan.  Where would Nyssa have gone?'
    'To find food?'
    'Exactly!  But she doesn't want to find innocent bystanders.  No, judging by the way you describe it, she's still almost herself.  She can just about keep her urges under control unless provoked.  What are the central facets of Nyssa's character?'
    'Erm, caring?  She care about people?'
    'True, which means she's not going to go hunting if she can help it.  Apart from that?'
    'Learning.  She always wants to learn things.'
    'Correct.  So she'll go to where she can find out more about vampires.  The headquarters of whoever we're up against.  Find that and we find her.'