An Errant Letter

Acquisition
In order to get this quest you need to:
 * Have started the Wayward Son quest.
 * Looted the Thrask's Letter from the abomination after you kill it.

Walkthrough
You simply need to return the letter to Thrask in the Gallows Courtyard. Your choices in the conversation with him effect on your future dealings with him, so watch what you say.

Result
If you decide to extort money from Thrask(which is 4 sovereigns), his demeanor will be different when you encounter him in the Act of Mercy quest. A more considerate approach leads to a normal XP gain(unavailable if you go for the blackmail) but no money reward.

Expect a smatttering of disapproval (particularly from Aveline) if you blackmail Thrask but a friendship boost with Fenris if you decide to hand over the letter and spare the templar the gruesome truth of his daughters fate.