The bony monster is on the same level as the imp that needs to be cured. Return to that level and check your map for any areas you missed, or rooms you could not get into.
<span class='standouttext'>Spoiler : </span><span class='spoiler'>If you head east from the room with the 2 imps, then take the southern corridor, there are a couple doors controlled by levers, that you have to split your characters up to get past.</span>
Another <span class='standouttext'>Spoiler : </span><span class='spoiler'>After you get through the 2 doors and explore that area, you will come to a locked door with no obvious way to open. All the other torches in the room are unlit, except for the one beside that door... click on the torch to put it out and open the room the bony monster (spider) is in.</span> (highlight the text to read)
