Sounds kind of like an old Errol Flynn movie, doesn't it. Actually, it's not quite that bad. The head is already dead.
Cosades wants information on the Nerevarine Cult and sends you to Sharn gra-Muzgob at the Balmora Mages Guild (she's the nice Orc lady down in the main room). He warns you ahead of time that she'll want you to do something for her, but assures you that it's going to be some trifle.
Sharn gra-Muzgob does, indeed, have an errand for you. She wants the head (skull) of Llevule Andrano from the Andrano Ancestral Tomb. Since Andrano is already dead, he won't be needing it for a while and gra-Muzgob has uses for it in the meantime.
gra-Muzgob's directions are pretty straightforward. You'll find the tomb just north of where the road from Pelagiad forks to Seyda Neen and Vivec. Since you'll have to walk, you can either walk from Balmora or from Seyda Neen, but it's closer to Seyda Neen. She gives you a few items to help you out:
She also mentions the Dark Elves' prejudices against necromancy. If you follow the "necromancy" conversation thread, she will tell you a little bit about necromancy as practiced in the Empire and in Vvardenfell. If you follow this conversation thread to "necromancers," she will assure you that she is absolutely NOT a necromancer and can't teach you any spells. Hmmmm.
Actually, she IS a necromancer, but you'll have a hard time proving it. If you can manage to unlock the chest next to her (requiring a decent Security skill and decent quality lockpicks) AND do it without her noticing (requiring a decent Sneak skill level), AND manage to snitch the copy of "Legions of the Dead" from within the chest without her noticing (also requiring a decent Sneak skill level), you can confront her with the evidence. If you fail at any of those three, she and the other mages in the room will attack you. If you are a member of the Mages Guild, you will be expelled. It makes you wonder whether a free spell is worth it. But be that as it may, when confronted with the evidence, she will confess to being a necromancer and offer to teach you either to summon a skeleton or summon a ghost free of charge if you will keep quiet about it. She will charge you to teach you the other one. Anyway, back to the quest.
The Andrano Acenstral Tomb is one of the larger Ancestral Tombs in the game. It's not huge, so it's difficult to get lost, but there are a lot of nooks and crannies, plus quite a few critters roaming about. So make yourself a saved game slot just before or just after entering.
As you enter, you'll be facing a long stairway down. At the foot of the stairs you'll find a dead Dunmer. He could have some decent stuff on him or not (don't you just love random treasure?). But there will be a roaming Ancestral Ghost somewhere in the vicinity.
Behind the door off to your left you will find a hallway ending in another door. Behind that door you will find:
I have found that the best way to deal with these two is to simply walk up to the door and wait for them to detect me, then stand back and Fireball the door. The Bonewalker will usually detect you first and try to get through the door. When you can see his hands and head sticking through the door (it won't open unless you open it), start slinging fire at him. For some reason, area damage done on one side of the door will carry to the other side. Once the Bonewalker is toast, it's a fairly simple matter to go in and bash the skeleton. Except for snagging the skeleton's arrows, there really isn't much of a good reason to mess with these two as there is nothing of value in their room.
Opposite the door follow a long hallway. At the corner, poke your nose around and see if you can catch sight of another skeleton archer. He's going to be just like the first one; his magical arrows will probably be different, but he's going to be shooting them at you. You'll either have to take him out with ranged spells or slug it out with him. He's got a buddy down in the chamber at the foot of the stairs:
Behind the door at the top of the stairs (you passed it on the way down to get the two skeletons at the bottom):
Through the door leading off of the chamber with the two skeletons in it, you'll find a hallway going down. Behind the first door in this hallway you'll find:
This is also where you'll find the Skull you were sent here to retrieve.
Elsewhere in the tomb you will find
Not bad if you still have the Strength to carry it all out. On the other hand, none of these critters will respawn, so you can always come back at your leisure to pick up whatever you left behind.
Upon delivering the skull to gra-Muzgob, she will tell you about the Nerevarine Cult and give you a copy of her notes for you to deliver to Cosades.
Deliver the notes to Cosades. His disposition will rise 10 points and he will promote you to Blades Apprentice. If you follow that conversation thread, he will give you one scroll each of Divine Intervention (teleports you to the nearest Imperial Cult Shrine) and Almsivi Intervention (teleports you to the nearest Tribunal Temple).
Cosades wants some time to consider what you've brought, so he suggests that you go back to doing Freelance work. You don't have to if you don't want to. Clicking on "orders" again will bring you your next mission, but a little time away from the toil and grind of the Blades might be just what you need.