Sacred Haven of Debauchery

Cleared out the Beholder's lair; it wasn't too difficult. I encountered some Kobold slaves there; almost all of them were mute (it reminds me of Asywind, haha). So, one of them told me about some caves that the Beholders don't like to go to, and where a Kobold found some interesting stone... Anyway, I took the stone and went to these caves (after killing all the Beholders), but magic doesn't work in this cave. I'm a wizard, damn it. Now I'm in a real mess, and to top it off, even potions and magical items don't work; all the bonuses are gone, and I'm overloaded. Dyken is acting stupid, trying to cast spells, but nothing works... Damn, he should just shoot with his crossbow. Well, at least we have Valentine with us; he's a good warrior and kills everyone. By the way, this cave is full of spiders (Lock: O), and in the main cave, there's a huge spider; I'll post a screenshot later...
I couldn't defeat it. I need to try to activate magic somehow; I don't know how. And I can't let my guys die because resurrection doesn't work there either. =[

P.S. In the screenshot, we're walking around in that cave.