Note: I made sure any bounty I had in Solitude was paid off before doing this quest. I recommend you do the same; just to make life easier on you.
First talk to Nazir to leave the move up to him, then leave the Sanctuary. Fast travel to Whiterun now and head to The Bannered Mane Inn , where we will find Amaund Motierre . He is surprised to see us alive, and even more surprised to hear that we’re still doing the contract.
Ask him where the REAL Emperor is right now and he’ll tell you that the Emperor is on his boat, the Katariah, near Solitude. You can also ask about Commander Maro and receive the OPTIONAL objective of " Kill Commander Maro ", and who wouldn’t want to do that!?
Commander Maro is at the " East Empire Company Warehouse ", the docks just south of Solitude. With your bounty paid off (make sure you do this) you can simply go TALK to him in plain daylight. He will be FURIOUS that you are still alive and will start to attack you.
You can now kill him and it will be considered self-defense. Well, that was easy. Go north now and find the Katariah anchored off-shore. Go swim towards it and find the anchor holding it down and you’ll see that it gives you the option to " Enter the Katariah ".
Once aboard you can handle the occupants however you want. The ship doesn’t have that many guards or sailors aboard, but does have quite a few locked doors and such. Personally I just killed everyone aboard since the sailors were easy prey and there was only 4-5 guards. The people to take notice of here is Captain Avidius and the head of the guards, Lieutenant Salvarus .
The reason to take notice of them is because they both have MASTER KEYS to the ship. Other than knowing that info, treat this area however you want. Go in killing, try to sneak through it, or sneak-kill everyone. It’s your choice. At the end your goal is the Emperor’s room after all. Just be sure to loot everything as you go.
Once you reach the Emperor he will ask you if you will let him talk for a bit. I personally let him. The Emperor has accepted his fate, but after some talking will ask you to kill whoever put a contract on him (Amaund). This will give you an optional objective of " Kill Amaund Motierre ". Dispatch your target and change history, then go back and talk to Amaund. You can use the "To Skyrim" door nearby and just swim away from the boat to lose any enemies and fast warp away (that’s what I did).
Amaund will be happy and will tell you your payment is in an urn where we first met with him (in Voluruud). Now you can close the doors to the room Amaund is in and dispatch him if you wish (it’s actually quite worth it, as Amaund has quite a few jewels on him). Just be sure you’re hidden **** to avoid a bounty (although this doesn’t always work - even with the door closed - so be prepared to be spotted).
Head to Voluruud now and take the first left to the room that we first met Amaund in. The urn here has 20,000 gold pieces for you! Jackpot!
Now go report back to Nazir to tell him of all that transpired, thus ending this quest. Nazir will tell us to make a visit to Delvin Mallory so that we may re-furnish the Sanctuary, starting the quest " Where you hang your enemy’s head… ". Also, if you hang out in the Sanctuary for a bit, the Night Mother will speak to you again, telling you to come talk to her.
This starts the quests " The Dark Brotherhood Forever ". Both are below for you to pursue. Also, did you note that the Brotherhood has two NEW initiates? Indeed, you can even have them come with you on your journey, making the " Dark Brotherhood Initiate " a COMPANION character.