The Whispering Door

Background
''Balgruuf the Greater, Jarl of Whiterun, has a troubled child. He's asked me to help the boy.''

Walkthrough
The Dragonborn must be at least level 20 and must have finished the main quest "Dragon Rising" to receive this quest.

Hearing a rumor about the Jarl's children at The Bannered Mare, and only The Bannered Mare, begins a miscellaneous quest to "Ask about Balgruuf's strange children". This requires speaking with Balgruuf the Greater. In the beginning, he is in Dragonsreach, but if the Dragonborn sided with the Stormcloaks in the Civil War, he is in the Blue Palace. When asked about his children, he reveals he is having problems with his youngest son, Nelkir, who has taken a sudden dark turn in his personality. This completes the miscellaneous quest and begins "The Whispering Door."

Nelkir is in Dragonsreach, even if his father is prisoner in the Blue Palace. After a series of disrespectful words and a few dirty secrets of Balgruuf's, Nelkir tells the Dragonborn how the Whispering Lady tells him secrets. He directs the Dragonborn to the locked door in the basement (the 'Old Wooden Door' or 'The Whispering Door').

Once there, when the Dragonborn listens at the door, a voice tells them that they are more worthy than Nelkir ("The child is spirited, but lacks... agency"). She reveals herself to be Mephala, and orders the Dragonborn to open the door. When asked how, she says that all of Whiterun is experiencing a severe case of paranoia, and that the boy knows of what she speaks. In order to find who has the keys, it is necessary to talk to Nelkir again. He says only Farengar Secret-Fire and Jarl Balgruuf carry the key, and adds that "no one will miss Farengar - I promise you."

At this point, it is necessary to find the Jarl or Farengar. If the Dragonborn sided with the Stormcloaks, then the Jarl is back at the Blue Palace, but Farengar is still at Dragonsreach.
 * It is possible to pickpocket Farengar through the map board in the side room.
 * Waiting for either Jarl Balgruuf or Farengar Secret-Fire to go to sleep allows them to be pickpocketed while sneaking without worry.
 * It is also possible to wait for Farengar to go to sleep, then kill him and take the key from his corpse.
 * If pickpocket skill is very low, a Paralyze spell, or Vampire's Seduction will allow pickpocketing the key with little effort.

After acquiring the key and unlocking the door, Mephala instructs the Dragonborn to take the Ebony Blade, which is next to a book warning of its corrupting evil.

Mephala now says the Ebony Blade does not match its legendary description, and has fallen to a lesser form due to its aging without use. In order to restore its former strength, it must taste the "blood of deceit". For the blade to do this, the Dragonborn must kill someone who trusts them: a person for whom a quest was done, or a follower. This completes the quest, although the blade still needs "charging."

People who trust the Dragonborn can be identified based on what they say. They may say something like "It is a fine day with you around", or "You've been a good friend to me. That means something." However, it is far easier to simply use a follower. Considering this, it may be easiest to use the Ebony Blade in the quests "Boethiah's Calling", "The Taste of Death," or "Lights Out!."


 * On the PC version of Skyrim, it is possible to resurrect killed followers or friends using console commands, allowing them to be killed repeatedly while reaching the Ebony Blade's full power.
 * One way is to find a beggar, give them a coin, receive the Gift of Charity, then kill them.
 * Alternatively, after completing all thane tasks and receiving all of the housecarls, they can be killed throughout the Dragonborn's households.
 * Another, simpler way is to acquire the Dead Thrall spell tome (random loot or purchased from Phinis Gestor), or activate the Ritual Stone, gather a follower and take them to an isolated spot, then kill and raise them repeatedly. This should minimize collateral damage and still raise the blade's powers.

Trivia

 * When inspecting the quest "The Whispering Door" more thoroughly with help of the Creation Kit, it is revealed that the quest was intended to be far more dark and elaborate. Unused scripts and packages hold references to all of Balgruuf's children having been intended to fall under the manipulation of Mephala.
 * One unused script named SF_DA08 Frothar Kills Horse Scene, shows that Frothar was meant to kill a black horse at the stables named Karinda, (currently an unused horse NPC). An accompanying script is named SF_DA08 Frothar Listens To Ebony B, referencing to Frothar falling under the control of Mephala much like Nelkir has, meant to occur at one point during the quest, with Ebony B standing for the Ebony Blade through which Mephala makes her voice heard.
 * Another script is titled SF_DA08 Children Kill The Jarl Scene, where Balgruuf's children were meant to gather at an undefined waypoint in secret, to commit patricide (possibly with the Dragonborn's aid as the script calls for removing Balgruuf's essential state). An accompanying interaction package is named DA08 Balgruuf Wait To Die In Scene where Balgruuf is present at an undefined place as to be murdered.
 * Upon Balgruuf's death, Hrongar was meant to replace Balgruuf as Jarl. Attached to his character is a lot of unused dialogue parallel to that of Balgruuf, meant to be used in the civil war quests and main quests. The dialogue varies from that of Balgruuf in that Hrongar takes a more aggressive approach towards the problems at hand.
 * If the quest is started and left alone, and then the "Battle for Whiterun" quest completed for the Stormcloaks, Balgruuf will no longer be Jarl and the quest may be lost.
 * If the blade is obtained beforehand by glitching through the wall and picking up the sword when doing the quest, the objective "retrieve the Ebony Blade" cannot be completed as the sword cannot be dropped and picked up again.
 * The blade can be placed on a weapon rack. Doing so enables the Dragonborn to "retrieve the Ebony Blade," thus completing the quest.
 * The keys to The Whispering Door do not spawn until after speaking to Nelkir the second time.
 * Despite Farengar being allegedly aware of the blade, it can be sold to him.
 * If the console command  is used on the whispering door, there is a cupboard behind the door that cannot be opened, and blocks entrance to the room without further usage of the developer console.
 * Upon further inspection, this cupboard is a placeholder for the Lady's voice.

Bugs
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