Hmm, you are on the right track, you need the sepent idol to reveal the book of Servants. I don't think that key is the skull key though, I think that one is called the Serpent Key (although my memory is getting stretched on that detail). You get that key off the high Priest Krueg - he gives it to you as a quest to cleanse the holds. If you "snuffed him" on sight, then as a quest item, the key should not have disappeared, but should be close to the body. If you are still having problems, then just post back saying so, and I or someone will tell you what the book of servants tells you to type in response to Xydusa's questions.
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