- Talk to Delphine in Riverwood.
- Meet Malborn in Solitude and give him any equipment you want smuggled into the embassy.
- Meet Delphine at the stables, wear the Party Clothes and hop in the carriage for a ride to the embassy.
- At the embassy, create a diversion and slip away from the party with Malborn.
- Recover Thalmor intelligence files from the ambassador's office.
- Go down to the dungeon and recover the rest of the documents.
- Obtain the key to the trapdoor and escape.
The quest entry in your journal states that you should meet Delphine in Riverwood. She will be found in the Sleeping Giant Inn, where you follow her back into her secret room.
Talking to her will reveal she has a plan to get into the Thalmor Embassy. She can arrange to get you into a party thrown by Elenwen, and that will be your chance to get some secret documents. You will need to speak with a wood elf spy, Malborn, who, although he isn't up to these kinds of high-risk missions, will certainly offer more than just a helping hand.
Meet Malborn in The Winking Skeever in Solitude. When you meet him, make sure to bring everything you want or need smuggled into the embassy, including amulets, rings, weapons, potions, etc. There is an Expert-Locked display case in Rulindil's office, so you may wish to bring lockpicks. Which items you should bring will depend on whether you wish to use stealth or combat. You have only one opportunity to hand over equipment for use in the Embassy. Everything you don't give to Malborn will be taken from you by Delphine to be stored in a chest in the Sleeping Giant Inn's secret room.
Following the meeting with Malborn, rendezvous with Delphine at the stables outside the city. She will make grave comments about your attire regardless of what you are wearing and give you Party Clothes that you must wear. When ready, Delphine will take all your remaining items and you will automatically board the carriage.
Once you have arrived, show the guard the invitation and head inside to be greeted by Elenwen. There is no rush, so you can take time to converse with the party guests if you wish. Depending on your travels, you may even recognize several of them from elsewhere in Skyrim and their dialogue will match accordingly. However, in order to slip out and investigate the embassy, you'll need to create a distraction. There are at least five options to cause a distraction:
- Order a drink from either Brelas or Malborn, and offer it to the drunkard seated on a bench to the left of the entrance.
- Talk to Erikur. Afterwards, he will hit on Brelas. Offer to talk to her for Erikur, and then do so. Go back to Erikur, and either response will cause him to make a scene, with Brelas carted away to the dungeons.
- If you have met Jarl Idgrod Ravencrone of Morthal and completed her quest, she will offer to be a distraction and start ranting and raving like a crazy person at the man sitting on the bench, allowing you to move on.
- The fourth option is to ask Ondolemar to cause a distraction with the man sitting on the bench, but only if you have completed a quest for him in Understone Keep. Keep in mind that he will attack on sight if you try to interact with him after completing the quest.
- If you've completed the quest Rise in the East, you can ask Orthus Endario to cause a distraction with the drunk man sitting on the bench.
You must now locate and retrieve documents with information on dragons. Approach with stealth and avoid detection, or charge in with combat and kill anyone who stands in the way. Proceed through the door on the left - you can either wait until the soldiers finish their conversation and move away, or kill them. Once inside, go up the staircase. A Thalmor Wizard will be standing guard ahead, facing the wall. Either kill him or sneak behind him. Head left down the hallway and left again to find the door leading outside. There are several guards patrolling outside, which can be easily evaded. However, a wizard stands guard at the door to Elenwen's Solar and will not move away. Either create a distraction to move him away and quickly dash in, or kill him. If you are seen, the guards will sometimes not follow you into the Solar.
Inside the Solar, there is a soldier immediately ahead who will head upstairs. Head to the left side of the room and search the chest behind the desk. Grab the dragon report and the two dossiers. There is a Stone of Barenziah upstairs in the bedroom to the left, required for a certain Thieves Guild quest, although if you have installed version 1.4 of the Official Skyrim Patch, the gem can instead be found later in Reeking Cave. There is a safe in a small room next to the bedroom with high level loot.
Go down the nearby stairs to the Interrogation Chamber. Rulindil and a Thalmor Soldier will be torturing a prisoner, Etienne Rarnis, in one of the cells. You can simply sneak behind Rulindil, grab the dossier and sneak into the cell or kill both him and the guard. You can also speak to the prisoner, who will tell you to escape via a locked trapdoor. You may free him if you so choose. If you caused Brelas to get arrested earlier, she will be in the cell at the far end and can be freed as well. She will assist you in taking out any hostile guards before escaping.
Once the prisoner has been spoken to or the document has been retrieved and read, two soldiers will enter the room with Malborn and begin to search for you. Either kill them and loot the key to the trapdoor, or pickpocket it from them; the latter option is difficult since they are constantly alert, but this is the only way to get through this quest without directly killing anybody (Etienne Rarnis' and Malborn's fates due to you not helping them notwithstanding). If you are inactive too long, they will kill Malborn, though this does not affect the quest at all. Go through the trapdoor.
The first area you need to pass will be just after the kitchen. There will be two guards having a chat there. Wait for them to finish. They will turn their back and walk away from you. The two guards are of different levels. The one with lower level will stay around the bar. He can be affected by Fury, but the other one will not. Once he is killed by his colleague, loot his armor and wear it, then go upstairs to find a wizard. He only looks in one direction. Walk, don't sneak, from behind. Since you wear the Thalmor's armor, he will think you are one of them. Proceed to the door to get into the second area.
This area is outside. Right after exiting from the corridor there will be a guard to your left. As you are wearing the same armor as them, he will say that you're new, but getting too close will cause him to attack. Sneak and cast Fury on him. He will be killed. After that, loot his bow and arrows if you have none - they can be used as distractions by shooting somewhere empty. The other guard can also be affected by Fury and killed. The wizard is, however, blocking the door. The easiest way to get past him is to summon something while hidden from afar. He will attack the summoned creature and you can sneak into the door. Although the eye will be open and say you're detected, he will not attack you for the moment. Proceed to the room with the quest marker.
The first guard you see will not detect you for a moment as he is not facing you. He will go upstairs. Follow him upstairs. When you enter, Rulindil will be speaking to a man named Gissur. When they are done talking, Rulindil will exit to the interrogation room and Gissur will eventually leave through the front door. Wait until then and you will only need to sneak past one guard into the dungeons.
In the dungeons, you can easily sneak to the chest. Read the book and it will point to the exit. At this point, violence is the only way to save Malborn and the prisoner, Etienne Rarnis. A key needed to exit may be pickpocketed from Rulundil, but exiting silently would involve abandoning the prisoner and Malborn. The key can also be obtained by looting Thalmor bodies. Note that if you use Fury on any of the guards, the situation will get out of control. Malborn will attack with his fists and will be easily killed by Rulindil and the guards, although it is possible to save him.
The trapdoor in the dungeon leads to Reeking Cave. There is a troll inside the tunnel who will attack the prisoners as well as the player, but you can simply run for the exit to avoid it. If you have any followers at this point they will be at the tunnel exit already fighting the troll. There is a necromancer's body, an Illusion skill book and an unusual gem beneath the ledge that you walk out on when you exit the tunnel.
Return to Delphine in Riverwood with the information you have obtained.
