In the realms of Hammerfell, a series of assassinations have been going on. Several members of the Hammerfell nobility have been killed, even some members of Hammerfell's religious orders. It has been believed the Thalmor are behind it, and so the party is sent to Sentinel to talk with a friend of Svarog, the Caliph, in order to help bring these assassinations to an end.
After talking with the Caliph, they are introduced to Favis, the leader of the Forebears, and Jabal, the leader of the Crowns. As leaders of the two major political parties of the Caliphate of Hammerfell, they are the ones most involved in the investigation of these assassinations. They ask the party to journey to a city called Abah's Landing, where it is believed there are some Thalmor hiding out.
The party goes to Abah's Landing and finds that the whole town has been subverted. Those that are not simply confined to their houses in fear have been arrested and put in prison underneath the city. The Thalmor are then using magical items called Hats of Disguise to impersonate everyone they have imprisoned and run the town through those disguises. After freeing the prisoners, including the Emir of the city, they discover some paperwork describing the Thalmor's efforts in hiring assassins to take care of a list of people. These people are all leaders of other cities and include the majority of the leadership in Hammerfell. While the people seem to have their own views of it being a ruse set in place by The Forebears or The Crowns to dispose of the other, there is an almost equal number of individuals from both parties on the list of possible targets. The recipient of a lot of these missives from the Thalmor is an individual named "Far." Loup, as a Redguard, knows that this is a Redguard word that means Rat.
The party journeys to the Sultanate of Ska'vyn, where they stop in the capital city of Skaven. There, they do a little searching and a bit of research and discover that there is a Dark Brotherhood Sanctuary in the city. They hunt for it and plumb its depths to look for possible answers. Within, they find some Dark Brotherhood Assassins who are Wererats. Within the Sanctuary, they find more letters addressed to Far, and begin to look for the targets of these assassinations to make sure they're ok. With Loup being familiar with the people of Hammerfell, they send a message to a Sultan in Elinhir to warn him of being a target. They then pick up and travel to Satakalaam, where Loup has a closer friendly tie with the Sultana; Shelaria Lupe.
An assassination is attempted on Shelaria, and succeeds. However, Valaya is able to resurrect her. Allowing the city to believe she is dead, so that the Assassin believes in his success, Shelaria travels with the party as they head north. In Upper Craglorn, they find a traveler, nearly dead at the hands of Thalmor. After rescuing him, and learning of their adventures, joins them in hunting down the Thalmor.
In the ruins of another Old Orsinium, the group finds a Thalmor contingent, with another Emissary. They fight and kill a bunch of Thalmor troops, an Orcish Barbarian, and Althír, the Thalmor Emissary responsible for sending out these contracts to 'Far.' With notes saying the Thalmor should gather and consolidate into the ruins of a city called Skyreach, the party follows.
Skyreach is an old, magical city with rampant magical effects still present within its walls. As they explore the city, they are constantly subjected to shifts in gravity. And amidst all of that, they find themselves in a fight, with not just Thalmor and Dark Brotherhood, including Althír, alive again because of the Clone spell, but also The Orcish Barbarian again, and Althír's wife, Yliel. On top of all of that, there was also an ancient figure, calling herself The Wolf Queen, and an incorporeal figure seemingly targeting the Dark Brotherhood.
At the end of the fight, a portal to Oblivion was discovered, and so the party went through to confront what was on the other side and had to deal with a few Dremora Kynreeves in order to close the portal.
With all of this done, they performed the Black Sacrament and went about putting a contract out on Althír and any remaining clones he had, in order to get him taken care of, while they would focus on finding Far, to put an end to the assassinations in Hammerfell.
Through some information, they made their way to a small hamlet called Kavzar. There, they found the brother of the current Sultan and Emir of Skaven. Putting pieces together, and searching through a faux-Brotherhood Sanctuary, they came to the conclusion that Sultan Hosni Hassan was, indeed, the person known as 'Far.'
Returning to Skaven, they faced Far and disposed of him. With Far slain, and with Althír marked by the real Brotherhood, Hammerfell could devote its full attention to helping Svarog in the war.