It's been years since anything really horrible has happened in the wizarding world not since you-know-who was defeated by the boy who lived. Sure, there has been fights breaking out from time to time good against evil but nothing drastic enough to start another war.
What has happened to the boy who lived and his friends you ask? Well, he settled down with Ginny Weasley and is Head Auror at the Ministry Of Magic. Ron is also working as a Auror with his best mate. As for Hermione, well, no one really knows not long after the war she just vanished leaving just a note saying "I'm Sorry" left for Ron. The only person who knows how to reach her is Professor McGonagall.
For the past few months there have been signs that something is brewing but no one knows exactly what, or who, it is and it has the people working at the Ministry worried. Trying to keep it under raps until they learn more. But Professor McGonagall has learned from the past so she has reached out to the three people who might be able to help out again.