I had an idea to have kidnapped kids, like really advanced ones and young adults with some kind of organization to essentially "better humanity" by more or less selective breeding, like natural selection but specifically chosen by a third party to make a stronger, smarter human based on DNA. They prefer to kidnap young people, but have perhaps kidnapped some people in their 30s or 40s, not well know professors but very intelligent people, possibility some athletes. Possibly if The Doctor starts getting his memory back and does something really smart he could get kidnapped. 

Anyways, throwing ideas at the wall to see what sticks. Sorry it took so long, sorry the response was short.