The Silver Hand

Background
"I have ascended to the Circle which leads the Companions, and now share their blood as a werewolf. To celebrate my new status, Skjor and Aela have invited me to attack a Silver Hand camp nearby."

Walkthrough
This quest allows you to become a werewolf. Becoming a werewolf increases your health and is reversible if you care to dabble in the transformation.

To start this quest, either speak to a Companion, or go to Farkus, and ask him for a job. He will then direct you to see Skjor. There’s a pretty clear outline along the rock wall that indicates where the secret entrance is. Head inside the Underforge, and when you’re ready tell Skjor to begin the ritual. After loading, you are out in Whiterun, and everyone is alerted. You can wait for the effects to wear off or wait until your health bar is depleted, upon which you are knocked unconscious. (There may be a difference from this description in the PC version, or an update has changed this; upon transformation, you are still in the underforge and can exit to the city proper, or use the one-way exit to the countryside to the East of Whiterun. Map, inventory, and most other actions are not available in Beast form, but the experience will persist, so map points discovered and foes killed will be there should you return in normal form.) When you come to, you will have already reverted to your human form, although you can transform into a werewolf by selecting Beast Form under Powers in the Magic menu (keep in mind that you’ll hit a cooldown period).

Aela mentions a Silver Hand camp nearby that must be exterminated. There is no specific way this "dungeon clearing" must be accomplished.

A straightforward approach is to head into the stone bunker at Gallows Rock, pull the chain to lower the gate, and make your way to the leader, Krev the Skinner. In the fight, Krev is accompanied by three archers; take them out first and focus your attacks on Krev to dispatch him.

Speak to Aela afterward to finish the quest.

Bugs

 * After participating in the ritual you can get teleported outside of the cave in Werewolf form, you can go back in and wait a couple of hours to get quest going to the next stage at Gallows Rock. Also you can go back into the underforge, and then leave through the back exit. After a few seconds you will be teleported to Gallows Rock.
 * Occasionally after the screen goes black when you are returning to human form, it may freeze and the player will have to load a previous save.
 * If you have a companion, it will disappear and Aela will take it's place. After finishing the quest your companion won't appear. If you return to where you first hired your companion, you will find them.
 * Skjor may not show up at the underforge,and you will not be able to do the mission.
 * Sometimes after transforming, when you wake up with Aela, your camera will be stuck in third person and not allow you to go back into first person view. FIX: Transform into a Werewolf again and wait for it to run out. Once in human form, wait a few seconds and then try switching to first person.
 * Aela may never enter the Underforge. Wait 24 hours then rejoin Skjor at the forge. The quest will then proceed as normal.
 * After talking with Skjor, if it's during day time, sometimes if you wait until night both Aela and Skjor will not talk to you at all, even after waiting more than 24 hours.
 * If you choose to simply re-enter the under forge after transforming, and try to leave out the back entrance, if you black out before you leave, the text "Enter Skyrim" will remain floating on your screen.
 * If you leave Gallows Rock without asking Aela what to do next, she will disappear and the player will have to load a previous save to continue on in the quest line.
 * While fighting the Silver Hand as a werewolf the game will sometimes switch to first person and you will be unable to act for a few moments - believed to be due to the slow motion kill not executing properly while a werewolf. Your weapons may also become recharged after the ordeal.
 * If you leave Jorrvaskr at the same time as Skjor, Skjor may fly to the opposite side of Whiterun, (near Uthger the Unbroken's house).
 * If you go to Gallows Rock and complete it before finishing this quest, it will make this quest unfinishable; therefore, making the Companion questline impossible to complete.