The objective for this quest is to loot a safe and set three beehives on fire to send a message to Maven Black-Briar, owner of the Goldenglow Estate, about what it means to cross the Thieves Guild.
Follow Brynjolf to the Cistern and listen to the full briefing by Mercer Frey. Speak with Brynjolf afterwards and he’ll suggest you go and talk to Vex. Go and speak with her and find out about the sewer that leads to the back door of the Goldenglow Estate. Don’t forget to talk to Tonilia to get your guild armor set before you leave. Bring plenty of lock-picks and a few torches to burn the beehives with.
If you decided to make your way there through the sewers, you’ll have to kill a few Skeevers along the way as well as avoid a fire trap. If you follow the marker leading to Goldenglow, you’ll exit next to the estate’s back door. Pick the lock and go inside. Move from room to room, silently sneaking by the guards. Consult your local map to find the marker and head to its direction to find an iron bar door. If you want, you can get the key to the safe from Aringoth himself, whom you will find on the second floor of the estate. [Persuade] him or kill him. You can also pickpocket or loot the cellar key from him.
The cellar door can be bypassed either by picking the lock or getting a key from a guard (or Aringoth himself). Continue to the basement and make your way over to the safe. You can open this easily if you have the key to the safe, otherwise your lock-picking skill will need to be quiet high. After emptying the safe, open the nearby iron door and head back to the sewers.
Head outside to the beehives and equip one of your torches (or a flame spell). Set fire to ONLY THREE of the hives. If you want, you can hang about afterwards and fight the guards or just run away in the typical manner of thieves. Head back to the guild and talk to Brynjolf to complete the quest and receive your reward.