Lady M's Diamond Caper 9/11

From the introduction: Take the small sealed parcel from Ambrose and place it under the specific orchid, in an arboretum in a specific mansion house. Not the weirdest job I've had but still - a bit unusual. Mind you, in return Ambrose won't kill me, Franz or any of our friends that he listed - just how did he know about them all? Who is this guy?