The Silver Hand
After becoming a full member of the Companions you can do additional quests for them. Eventually you will be told to talk to Skjor who will say that it is time for you to be inducted into the inner circle. He will ask you to meet him in a chamber under the Skyforge after dark.
The secret chamber is fairly easy to find; the entrance is obvious but you can’t open it without Skjor. Skjor will lead you inside where you will find Aela the Huntress waiting… in werewolf form. You will be told that in order to become part of the inner circle you must become a werewolf.
Aela will cut herself and fill a basin with blood. Drink from it to become a werewolf.
You will immediately turn into wolf form and return to the outside. As a suggestion, don’t leave the area of Jorrvaskr; the Whiterun city guards (and a number of civilians) will attack you on sight and you don’t want to kill anyone you don’t have to. Just wait a bit and you will eventually pass out.
When you come to you will be well outside the city with Aela watching over you (she has your equipment). She will tell you that you are near a place known as Gallows Rock; a stronghold of the Silver Hand. The Companions are planning to attack it in order to defeat a Silver Hand leader known as “Krev the Skinner”. (The reason for his name is left as an exercise for the imagination.) Skjor was also with you but he went ahead on his own while Aela was waiting for you to recover.
Collect your equipment and enter the caves with Aela. Fight your way through the Silver Hand until you reach Krev and kill him.
Once this is done you will find Skjor’s body, killed by the Silver Hand. Aela vows revengs.
Stealing Plans/Striking the Heart
Aela wants your help in getting revenge against the Silver Hand for killing Skjor. First, she asks you to go to a Silver Hand encampment and recover plans which will tell her where the Silver Hand leader is hiding. Once you have done that, she asks you to go to that place and kill the leader.
After killing the Silver Hand leader, Aela will tell you that Kodlak has learned of the vendetta the two of you have been waging against the Silver Hand and is unhappy about it. He has asked to speak with you.
Kodlak speaks briefly about the vendetta then turns to talk of his (and your) lycanthropy. He says that when a werewolf dies their spirit is taken by Hircine to join her in her eternal hunt and that while some of the Companions may welcome this as their eternal destination as a true Nord he wishes his spirit to go to Sovngarde. To do this, he needs to be cured.
He reveals that the Companions have not always been werewolves but became such after being cursed by the Glenmoril witches. He wants you to go to the Glenmoril Coven, kill one of them and return with its head.
The Coven contains five witches. You only need to kill one of them but killing more of them will give you more heads which can be used to cure others (including yourself) of lycanthropy as well. (If you kill all of them you will occasionally be recognized in towns as the hero who wiped out the Glenmoril witches.)
After getting the head or heads return to Jorrvaskr. When you arrive, you will find a crowd of townsfolk and Aela and another Companion standing over the fallen bodies of several of the Silver Hand. Upon going inside you will be immediately accosted by Vilkas who demands to know where you have been. While you were away the Silver Hand attacked Jorrvaskr. Kodlak is dead (as are several other Companions) and the Silver Hand has stolen the remaining fragments of Wuuthrad. Vilkas vows revenge and asks you to accompany him.
Purity of Revenge
Travel with Vilkas to Driftshade Refuge and attack the Silver Hand there. Inside you will find a number of werewolves in cages, most of which will actually attack you if you free them. (Yeah, you’re welcome.) Kill the Silver Hand and recover the fragments of Wuuthrad then return to Jorrvaskr.
There, you will find the Companions gathered for Kodlak’s funeral. Attend the funeral then give the fragments to Eorland. Eorland will tell you that Kodlak had a final fragment that he kept in his quarters. Go there and retrieve it.
While in Kodlak’s rooms, look around and find his journal. If you read it you will find that Kodlak had dreamed of your arrival, which is why he was so agreeable to your joining the Companions.
Return to Eorland with the final fragment and he will use the Skyforge to reforge the axe Wuuthrad. (Shades of The Lord of the Rings‘s Narsil.)
The Companions will decide that they need to honor Kodlak’s final request and let him enter Sovngarde. To do this, all of you will have to travel to Ysgramor’s Tomb.
Glory of the Dead
Travel to Ysgramor’s Tomb with Aela, Farkas and Vilkas. There you will find a statue of Ysgramor. Put the axe in the statue’s hands and a hidden door will open. Fight your way down through the tomb. (Your companions will drop out one at a time as they feel they cannot go further.)
At the bottom of a tomb is a brazier. Activate it and put one of the witches’ heads in it. This will separate Kodlak’s beast spirit from him (looking like a spectral ghost) and it will attack you. Defeat the spirit and Kodlak is freed. He will thank you and recommend that you be named Harbinger of the Companions then his spirit will depart for Sovngarde.
If you have more than one witch’s head you can cure your own lycanthropy here. Put a second head in the brazier and attack the wolf spirit to be cured.
After returning to Jorrvasker and doing some additional tasks for the Companions both Farkas and Vilkas will eventually ask you to help cure them of lycanthropy as well. Return to Ysgramor’s Tomb and repeat the process for each of them. Aela the Huntress apparently prefers to stay a werewolf.