I couldn't find (or think of) a better spot to ask about this; my apologies if there is a better place to ask. Semi-spoilerage below:
I was playing the module and got to the part where Sola gets abducted by the drow with plans of turning him into a drider. I'm in the tent, and activated the portal with the little mysterious stone. I found a big stone, which I assume is supposed to be used to weigh down the pressure plate and keep the portal open. However, no matter how I place the stone, the plate does not stay activated. Even with haste, I cannot run to the portal and make it in time. My only other game option is to turn back after meeting Cania and talk to the king, but that seems to speed up the plot way too fast and puts me at an endgame situation, it looks like (at least from first glance - you go to the castle, learn Cania's identity, big fight...). Any advice?