Cyrodiil/Upon My Honor

Quick Walkthrough
# Talk to   or   about  .
# Gather evidence on Harran's disappearance at  .
# Find Harran in the  .
# Return to Lassinia with news about her husband.

Detailed Walkthrough
Where's Daddy?
You can start this quest by speaking directly to  , but it's more likely you'll bump into her daughter,  , who will ask after her father as she catches her breath from running around  . She'll explain her father   is a soldier in the Imperial Legion, and that she hasn't seen him in a very long time. To keep all options open, ask her about both her mother and her grandfather,  , and speak to him first. It's clear he doesn't much like Harran, as he thinks his loyalties conflicted between the Legion and his Nord heritage. Next, head over to the   and ask Lassinia about her missing husband.

A Needle in a Snowstack
Lassinia will confide that her husband was stationed at   but that she hasn't seen in him in months, and all her letters have gone unanswered. If you agree to help, she will mark the fort on your map and suggest you start your investigations there. On arrival, speak to the commanding officer,  , who will inform you that Harran and a few other soldiers vanished after going out on patrol. He admits he hasn't had time to investigate the matter, as he's been dealing with   a  , but notes his soldier might know more.

Question soldiers patrolling the fort, and they will recall that there was only one survivor who staggered back from Harran's patrol. His final words were "Stormcloaks" and the soldiers will speculate the rebels managed to cross the border through the cave system known as the  , given that the   is locked shut. They will mark the cave on your map and send you on your way.

Up to his Ears
Enter the cave and at the first intersection, just to the left, you will find Harran's corpse in blood-stained snow, a   nearby. On his body is his  , which will help you piece together what happened in the last few months. Harran and his companions were on patrol when they came across five Stormcloaks hanging from a tree. They were meant to be taken for trial to the Imperial City, but were instead summarily executed by the Thalmor. After burying them, the soldiers came across the Thalmor and two more prisoners, and were attacked by the Elves. After dispatching them, some soldiers fled back to the fort, but Harran and the others joined the Stormcloaks and set up camp in the Trail, where he would eventually meet his end.

Hero or Traitor?
On the way back to Bruma, report your findings to Legate Varro, who will plead with you not to reveal the truth about Harran's betrayal. Once in the city, you essentially have three of options:
Breaking the news to Ellina about her father's death;
Telling Lassinia about her husband's death;
Informing Sellus of his son-in-law's death and treason.

If you speak to Sellus, you will only have the option of telling him that Harran had betrayed the legion. He will ask you for the journal, so that he may burn it and shield his family from Harran's shame. If you agree, he will thank you and reward you with 250 gold. If you choose to talk to Ellina or Lassinia, you have the option to either lie or tell them the truth - this doesn't have any effect on the final reward. Regardless of your choices (other than giving the journal to Sellus) and dialogue options, Lassinia will reward you with 400 gold for your efforts.

Notes
If you sided with Bjarni Shatter-Stone during A Stormcloak in Chains, you obviously won't be able to question the legionnaires at the fort and you will have to find Harran on your own, without the aid of a quest marker.

Quest Stages