This guide contains minor spoilers
After completing the Proving Honor quest, Skjor has decided that you have proven your worth and invites you to meet him at night near the entrance of the Underforge located just North of Jorrvaskr. Follow Skjor’s instructions as he explains the special “gift” that has been granted to the Companions and why the ritual that follows must be done in secret.
NOTE: Be careful not to kill any merchants in Beast Form as they will stay dead and you will no longer be able to barter with them.
Eventually, everything will fade to black as you pass out from the transformation; when you wake, you will be just outside Gallows Rock with Aela watching over you. Speak with the Huntress and she will explain that your transformation, though difficult, was successful. To celebrate she decides that you will slaughter a camp of Silver Hand followers nearby. Ask Aela any questions you will, then gear up and prepare for battle.
Storm the camp and dispose of any Silver Hand nearby before entering the doors to Gallows Rock on the ground floor with the two spiked wolf’s heads around it. Once inside activate the Pull Chain to lower the bars and work your way through the dungeon clearing out Skeevers and Silver Hand as you go. Be sure to have Aela along with you the entire time as she comes in handy in the ensuing fights. You can choose to release any werewolves you find alive and in cages, they will either attack the Silver Hand or (in my experience anyway) the nearest person to them.
Eventually, you will come across the last room in the dungeon filled with two Silver Hands as well as Krev the Skinner. Once they are all dead, Aela will notice the body of Skjor; he should not have come here alone. In order to continue the Companion’s Questline, you must now complete two more Subquests for Aela in order to unlock the quest Blood’s Honor.Skyrim Sidequest - The Silver Hand,