Valentine Morgenstern is starting to make his move in order to eradicate the Downworld and the Shadowhunters are currently oblivious to this.
Maybe the Downworld isn't.
Maybe they can fight back.
My High Warlock Jet Valentine (yes, the irony) and others have started to hear rumours and perhaps find evidence.
It won't be easy, but Jet would probably discuss this with fellow trusted Warlocks and so on, and slowly they can -inconspicuously- make a resistance against Valentine and his possible future posse.
What do you think?
And who would like to join Jet and the others (who wants to be Jet's co-founders of this 'group'? They have to be trustworthy and fairly sensible x]).