The doctors’ plot has us all wondering: What’s next? Crispin Black, a former government intelligence analyst in the U.K., has some chilling thoughts:

“The state needs to be more rigorous about those professionally qualified workers it decides to admit to this country. An advanced education is no safeguard against extremism. The Government must make sure that professionals – in whatever field – are vetted if they come from countries where there is a chance that they might have been recruited by extremists. Rogue engineers, for instance, could do enormous damage.

“How will al-Qa’eda mutate next? Two specific threats have worried the intelligence community for some time. First, that it will manage to recruit Caucasians covertly to their cause – not obvious converts who then adopt extremist positions, such as the American John Walker, who fought with the Taliban in 2001, but individuals who adopt an extremist mindset without any tell-tale signs.”