Loud and Clear

You are now part of The Thieves' Guild. Your first job is to finish a job that was left undone. The target is alert and will be expecting trouble.

Follow Brynjolf
Follow Brynjolf around to the back of the Ragged Flagon and into the Cistern. There he will walk up to the centre of the place and introduce you to Mercer Frey. Mercer will comment a bit on how Brynjolf better not be wasting his time before giving you a mission.

Listen to Mercer Frey
Mercer tells you that Aringoth, the supplier of honey to the Black-Briar Meadery in Riften has been getting a bit uppity lately. He has been supplying his honey elsewhere and Maven Black-Briar is not happy about that. The Guild has been hired to make an example of Aringoth by wrecking some of his production facilities as well as finding out where he got so much confidence from.

Talk to Brynjolf
After Mercer is done, speak to Brynjolf and he will tell you it was Vex and Delvin that botched this job before, so he suggests speaking to Vex to get some details on the target location. He also suggests getting yourself set up with a uniform, a Thieves Guild Armor set from Tonilia if you have not already.

Speak to Vex about Goldenglow Estate (Optional)
If you choose to speak to Vex, she will tell you exactly what went wrong with the job and inform you of a secondary entrance that you can use to enter the estate undetected.

Now the order in which you do the following quests does not matter.

Burn 3 beehives
The beehives are located on the westernmost island that makes up the Goldenglow Estate. There is a bridge to the west but there is no way to open the door except to loot the key from one of the guards. So make your way to the north-eastern side of that island and scale the rocks there. Once you are on the island, you can nick a torch from one of the guards or just use the flames spell to set the beehives on fire. Be warned, the moment you start, all the guards will come running and looking for you. Either try to fight them, or make a break for it into the water and they will forget you soon enough.

Enter Goldenglow Estate through the sewer (Optional)
The sewer can be accessed by going around to the north-west side of the easternmost island. There will be some docks there. The rocks to the right side of the docks can be scaled. At the top, you will be facing the back door of the manor. The sewer entrance is just to the left, hidden in some grass.

Obtain the key to Aringoth's safe (Optional)
If you are there at night (if you are not you really should be), Aringoth will be found on the top floor. If you entered through the back door (expert lock), you can easily make it to Aringoth's room without alerting any guards. When you see a bunch of mercenaries sitting at a table behind a bookshelf, turn left and enter the dining room. Once you exit from the opposite side, turn left again to go up the stairs to the top floor. Aringoth is in a bedroom nearby. Sleeping if you went there at night so pickpocket the key off him.

Clear out Aringoth's safe
At the base of the stairs to the second floor, the gate barring the way to the stairs to the basement should be right in front of you. It is locked though (novice lock) but should not pose a difficult barrier. Pick it and head down into the basement. In the first area, you will see two mercenaries in the far right corner. Continue on straight ahead towards a door. In this next corridor, there is a patrolling mercenary. Simply wait for him to round the corner and head down some stairs nearby. At the base of the stairs, turn left to get to Aringoth's safe. Now pick it (expert) or just open it if you got the key and clean it out. Close to the safe an exit will lead back to the sewer, to help make a quick escape.

Return to Brynjolf
When you have gotten the incriminating letter and burned the hives, make your escape from Goldenglow and head back to the Guild to find Brynjolf.