Prime Suspect

Acquisition
This quest is acquired by completing the companion quest Calling on the Captain. Speaking with Aveline will prompt her to ask you to keep Emeric quiet, as his relentless investigation into the deaths of young women (which was covered in Act I as The First Sacrifice) has caused the city guard to embarrass itself. Speaking to Emeric will continue the quest.

If you accept the quest along a Humorous line of conversation:

If you accept the quest by beginning the conversation with an Agressive or Humerous tone, but end Diplomatic:

If you accept the quest along an Aggressive line of conversation: ,

Walkthrough
Go to The Gallows to speak with Emeric, and he will ask you to go to Gascard DePuis' estate in Hightown to find evidence of his guilt as the murder of the young women. If you agree and go to the house you will find the place full of shades and other enemies. When you enter the final room you will find Gascard DePuis with an obviously abused and terrified woman. He claims to be the one that has been hunting the murderer, although he admits to resorting to blood magic in order to do it. You can either fight him or let him go.

if you choose the humor choice of "This I have to hear." in this conversation.

Whether you fight him or let him go, when you go to tell Emeric what happened there will be a Templar named Moira telling you that Emeric is ready to meet you tonight according to the note you gave him. Of course you didn't give him a note at all, it looks like a trap. When you arrive at the back alley where you told him to "meet" you there will be shades and abominations and a dead Emeric. The templar you spoke to earlier will arrive after the battle. The quest ends at this regardless if you choose to kill Gascard or not. Emeric dies either way, it is not possible to save him. The follow up quest is All That Remains which is acquired later in Act 2 from Hawke Estate.
 * If you tell her you killed Gascard (Who is obviously not responsible for the murders and was telling the truth) she will tell you there is a dangerous mage about that Meredith will want captured and run off.
 * If you did not kill Gascard you can either implicate him in which case the Templar tells you she will inform the city guard and Gascard DePuis will not escape the city alive. Or clear him and she will say that they will have to continue investigation that Emeric started, considering he was right and died for it.
 * Implicating Gascard may lead to his execution, off-screen, by the Templars. This restricts your options for completing the following quest, All That Remains.

Result
If you allow DePuis to live: ,,,.

If you romance Fenris or Isabela they dont seem to care. No rivalry.

My character is in romance with Isabela (I have here friendship). But received a.

-Grouped with Aveline, Varric, and Merrill, with Aveline and Varric at full friendship and Merrill at circa 30%, no rivalry or friendship was gained or lost, after asking all available questions, and picking the diplomatic option "Emeric will want to know about this". More than likely, the extra diplomatic dialogue choice prompted from one of the questions was able to negate any approval loss from Merrill. (This negation of approval loss does not work for Aveline if Hawke has developed an Aggressive personality throughout the game to this point)

Rewards
The XP payout is in the 1300-1600 range. You gain roughly 1900 more exp if you decided to kill DePuis from the fighting in his mansion.