I have four monkey idols and placed them correctly in the library to activiate the lift. I dont have a serpent idol. I am struck now. There are only two place I cant go. one is a door that wont open located somewhere in the centre. Second is a gate that dont have a lever on my side of the wall. It's location on the right side of the serpent head and all the way following that path. I need help!! Can someone tell me what to do next? By the way, what is the prisoner for?

Need the back door entrance after coming up the ramp you might recall finding an area described as snake/serpent holding pens. You need to enter that area. At the back of those rooms there is a water area you can enter. Follow the underwater passage and it will lead you to a small room where you will find the snake idol.

I'm trying to remember which key it is you need to get into this area. When I think of it, I'll repost.

Wyv

You need the serpent idol to open the secret door in the big statue in front of the brazier. It is hidden under the back door, go via the serpent thingy rooms nearby

The prisoner will tell what to do, (use the red hot poker on him).

The gate near the library can only be opened from the inside and the gate by the back door with the naga behind cannot be opened at all.

You need Kreug's key to open the pens.

The prisoner serves two purposes. He is the goal of a quest (you give him his picklocks) and he also tells you a bit about the evil mask which you will need later in the game.

Wyv

Astyanax can tell you how to get information out the prisoner by using the red hot poker.

Now that I have the serpent idol and the book of servant, where am I to go next?

Go chat to the prisoner. He has loads of information - if you treat him right (hehe, I just love that poker!)