At the Lair of the Devourer, you'll be matched against the Head Gaoler Aleafin himself (or what's left of him anyway). Now, since I believe in saving everyone *cough* Yeah right *cough* I persuaded the jail guards in the Lair to snap out of their stupor. However you can choose not to do this and kill off the guards one by one. It depends on how you want to play this, as of course more death means more experience.
Anyway.. on to battling with Alaefin. If you've managed to disperse of the guards (a successful persuade check will snap them out of their stupor) before hand, Alaefin will be your second to the last battle for this area. Second to the last you say? How can that be? Well dear player, once you've dispatched of the puppet, its time to lay waste to the Puppet Master - in the form of the Intellect Devourer.
Kill it, grab everything you need to grab and return to Aribeth with the reagent. (Oh and don't forget to say hey to all the people who are waiting for news at the Peninsula District). When you're done with this, its on to move on to the Beggar's Nest and find some undead!