In 1977 there was a great film made starring #CharlesBronson, Lee Remick and #DonaldPleasance, the film is http://www.imdb.com/title/tt0076804/
The concept of the film is that "sleeper agents" are sent under cover into an enemy territory. These people who are well trained, live ordinary lives and gain respect, until they are activated sometimes by coded messages as in my e-book https://www.draft2digital.com/book/148423, or by telephone as in the film.
At the time of the film, the threat was the growing power of the Soviet state, the threat today is #ISIS. If you think I am exaggerating the threat, consider this. Last week, the German govt announced they'd lost track of over 600,000 Muslim immigrants http://www.nowtheendbegins.com/germany-cannot-account-for-600000-missing-muslim-migrants/.
My theory is the Germans didn't lose track, these people are being hidden in sleeper cells with the Muslim communities in the cities of Southern Germany, waiting for their next target to be chosen.