Beside the locked door on the level with the imp brothers (east then south from them), you should see a lever. Pulling that lever will open that door, and close the door after it. Past the second door there is a second lever....
<span class='standouttext'>Spoiler : </span><span class='spoiler'>Your two characters will have to split up temporarily...</span>
BTW, you definitely want to complete this quest. <img src="/ubbthreads/images/graemlins/biggrin.gif" alt="" />
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