[Melusine]

Possible Curst Prison spoilers ahead....
'
'
'
'
'
'
'
I'm in Curst Prison, have talked to Trias, got the sword from Cassius and freed the deva. I know that Vhailor is in the locked room in the north east but how do I get there?? Before freeing the deva, all I saw was a locked door that I cound't bash in/lockpick, and now that the portal is activated I cannot open the door as the only options are "go through portal" or "leave". How do I enter the room where Vhailor is?? Have I done something wrong along the way?
I tried looking in several walkthroughs, but all they say is "walk round the portal"... HOW?