The empty canal.
Warning from an Anonymous Friend is a written note found in The Brigmore Witches.
Transcript[]
Hello friend,
As instructed by your Whalers, I have dredged this horrid thing up from the depths of the storm drains and placed it in the agreed upon location in hopes that you, and only you, recover it.
But be warned, poor fortune has followed me every step of the way since laying hands on this thing, and I am overjoyed at the prospect of leaving it here and being done with it. May it treat you better than it has me.
And if some unlucky local has stumbled upon this wicked bone, heed these two warnings: As I have said above, poor fortune will find you. But more importantly, this is intended for delivery to the most dangerous man in the Empire. If you are in possession of something he wants, you may count your remaining hours on one hand.
Location[]
It can be found near the storm drain in the empty canal during the mission, The Dead Eels, if Daud purchases the "Hidden Rune" favor.