- Talk to Brynjolf in Riften or talk to the Argonian bartender in The Bee and Barb.
- Search the Ratway for Esbern's hideout.
- Find Esbern in the Ratway Warrens.
- Talk to Esbern.
- Bring Esbern back to Delphine at Sleeping Giant Inn in Riverwood.
After infiltrating the Thalmor Embassy, return to Riverwood and inform Delphine of what you learned from Thalmor records. The task now is to retrieve the archivist Esbern from his hiding place in Riften, and you're given a code phrase to say to him.
The player's journal will direct you to talk to Brynjolf. You may speak to him or Vekel the Man inside The Ragged Flagon; both give an option to Persuade or bribe them for information on Esbern's location. He will tell you that Esbern is located in the Ratway Warrens. As the location is accessible before this, you have to the option to proceed directly to Esbern without talking to them. The quest continues as normal and will update with both finding Esbern and talking to Brynjolf. Thalmor are still present in the Ratway regardless.
The sewers and tunnels beneath Riften are inhabited by a number of thugs and three or four Thalmor warriors searching for Esbern. When you reach the door to Esbern's room, he is very wary of Thalmor agents and initially refuses entry. You may persuade him by saying Delphine sent you, you can tell him the password "where were you on the 30th of Frostfall?", or you may state that you are the Dragonborn.
Once he is convinced that Delphine sent you, he tells you what he knows: Alduin World-Eater's return has apocalyptic implications, and his warnings of this threat have been consistently ignored. He agrees to follow you to Delphine's base in Riverwood.
As soon as Esbern leaves his hovel, more Thalmor agents show up and attack. Esbern is a capable mage, summoning atronachs whenever engaged in battle. Exit back to Riften through the Warrens. While escorting Esbern through Riften, watch out for Gissur and Shavari (hired informants for the Thalmor), who will likely attack.
Leave Riften for the Sleeping Giant in Riverwood. You can fast travel if he is following you. Also note that if you asked him to show you the way out via the "Do you know the way out?" dialog option, he is not following you and you must have him wait and re-follow or he will potentially get stuck on the way out and additionally will not automatically show up with fast travel the way followers do.
Once he is reunited with Delphine, the next quest begins.
