Mr. Black was sent by The Agency, of course. The Agency needs to make sure these other Fables aren't secretly being manipulated in an insidious plot by The Agency to take down The Agency using The Agency as a smokescreen. 
He has other tasks, though. For one, he needs to find Mr. Black, who is suspected to be working with Mr. Black as a quintuple agent for The Agency against The Agency. Third would be answering the question: Who is Mr. Black?

Also I followed rule 6 when I made the sheet. ctrl+f if you don't believe me.