Online:A Tale of Two Mothers

Quick Walkthrough
#Talk to Lanarie in Shimmerene.
#Talk to Talerion in Kinlady Avinisse's Mansion, and grab a copy of Arathel's Map.
#Find the correspondence in the hedge maze east of the Ruins Bazaar, and choose whether to report it back to Talerion right away, or follow it to the nearby Anchors Aweigh Inn.
#In either case you will be pointed towards the sewers of Shimmerene, and told to look for the Mother of Rats.
#Follow the unique rat in the sewers, find the false wall that hides the hidden lair and talk to the Mother of Rats.
#After learning about her organisation of outcasts, and Mirulon's rival organisation, find the Mother's associate Zan'hi, who is currently spying on Mirulon's gang.
#Talk with Zan'hi to learn that Mirulon is a Daedric-summoning sorcerer with mind-control abilities which he may use if Arethel continues to refuse his orders.
#Follow round the tunnels, find Mirulon and kill him, then read his notes and catch up with Arethel.
#Escort Arethel back to the Mother of Rats - who has been joined by both Lanarie and Talerion.
#Hand Mirulon's notes to Talerion to exonerate Arethel, and receive your reward form the Mother of Rats.

Detailed Walkthrough

On the way to the Monastery of Serene Harmony (as required by the first quest in the Summerset plotline), you will encounter Lanarie. She is concerned about her missing son Arathel, who is apparently involved in a plot to kill the Sapiarch, Aicantar. He has turned himself in to the authorities, but subsequently gone missing: Lanarie suggests that Talerion, the Justiciar in Kinlady Avinisse's service, may know more about his disappearance than he is letting on.

Entering Avinisse's mansion and going downstairs reveals that Talerion seemingly does not know much: he is less concerned about the question of Arathel's guilt or innocence, this being a matter for his trial, than he is about the actual fact of his disapperance from custody (which he regards as a major embarassment bordering on disgrace), apparently through a hole in the wall that leads to the sewers.  Apparently a map was found on Arathel at the time of his arrest: and a copy is kept upstairs, which his own officers have failed to make much sense of. Examining this map leads to an area further in the north and west of the city, a hedge maze not far from the Ruins Bazaar and Anchors Aweigh Inn, where a letter to Arathel has been dropped. Reading the Note to Arathel suggests that Arathel has friends, and that they include a Khajiiti bartender in the nearby inn, at which point the player has the option either of reporting directly back to Talerion or following the conspiracy further by talking to the bartender (named Riharai) and ordering a "Deathland Ale".

If the player talks to Talerion, he will suggest that the Mother of Rats may be involved with the letter - she is an outcast who lives in the sewers, associating with the worst of Shimmerene's outcasts, rogues, beggars, apraxics and general underclass. If the player talks to Riharai the bartender - and subsequently to the hooded man upstairs - then they will also be pointed towards the Mother of Rats: in either case, the player enters Shimmerene's sewers, albeit through a slightly different entrance, and has the same objective, to track down the Mother of Rats. Talerion will paint her in a suspiciously sinister light, viewing her and her organisation as undesirables who have so far been tolerated as being comparatively minor, but if they are involved in the plot to kill a Sapiarch then they may be a greater threat: Riharai and Edgar will present her in a more sympathetic light, as one who cares for the outcasts when nobody else will.  

Whichever route you take into the sewers, you will fight various conventional sewer monsters (such as skeevers and salamanders) and thugs from an organisation called the "Black Wake": you will eventually encounter a unique Rat which will run away as soon as you approach it (it is sometimes difficult to follow because it can go throuh small gaps that a rat can fit through but the player cannot, forcing you to find a longer way around to follow him back to the quest arrow), eventually leading you to the false wall that hides the way into the room in the southeastern corner of the sewers, where the Mother of Rats lives.  She, in turn, will talk of Arathel as an idealist looking to improve the lot of the underclass, who was originally working with the Mother but has now fallen in with a rival gang (the Black Wake, whom you have already been fighting), led by one Mirulon who apparently seems to be wanting the violent revolution that the Mother of Rats would in fact rather avoid. It's suggested that Mirulon is the real master of the plot to murder the Sapiarch, and Arathel got involved in it but got cold feet and turned himself in. It is apparently Mirulon who sprang Arathel out of jail but is now holding him prisoner: the Mother of Rats has one of her associates, a Khajiit named Zan'hi, spying on Mirulon already, and the player is sent to look for him.

Zan'hi can be found in the southwestern natural caverns, talking to another Khajiit - Hedani, his lover, whom he tries to persuade (successfully) to abandon Mirulon's cause, to which she seems to have become attached.  You will interrupt their conversation, and learn that Mirulon is more dangerous than he seems - he is a sorcerer with a penchant for Daedric summoning, and is prepared to use mind-control magic on those who defy him, which means he may be no mere anarchist or revolutionary.  Follow the caves around until they rejoin the sewers to find Mirulon's lair:  as you arrive, you will overhear a conversation between him and Arathel in which Arathel still defies Mirulon's orders to commit the murder, and Mirulon threatens that he will do it whether he wishes to or not.  Mirulon attacks as soon as you enter the room: Arathel makes his escape. After Mirulon is dead, find his notes - apparently referring to masters called "The Earls" and signed "In Oblivion's Name", confirming Zan'hi's suspicions that Mirulon's motives are more sinister than a question of mere mortal anarchism or revolution. Follow the sewers round to find Arathel and escort him back to the Mother of Rats.

When you get back there, you will find that both Lanarie and Talerion have also found their way to the Mother of Rats's chamber. Arethel is greeted first by his mother, while the Mother of Rats directs you to talk to Talerion: who is sceptical at first, but accepts Mirulon's notes as proof of a wider plot, possibly Daedric-related, and as evidence good enough to exonerate Arethel.  He still disapproves of the Mother of Rats, and disappears with a warning to keep her affairs in order now that he knows where they hide out, while both Lanarie and the Mother thank you for the rescue of Arethel and reward you with the "Rat-Fang Dagger" - a dagger with a poison enchantment and the Precise trait. 
 
 

Quest Stages