Off I went to the bit where the acid water was, and as expected, it became normal water again. I then worked my way through quite a few lizardmen, ice women things, and some witches, before finding a huge ice demon thing which killed me.
So I tried again, took a slightly different route, and found a save point. Just past that, was the next boss – Camilla (who is the woman right at the start of the game who is trying to resurrect Dracula). We had a little chat, she implied that Hugh has become a follower of Dracula, and then turned into a winged devil woman riding a giant skull. And killed me.