Unfortunately, there is a bug here that screws up the sorcerer's ability to get the pond scum from the fountain for Jerrod if the player has already gotten the old water and the lily from it earlier. It's supposed to just be Hand on fountain that allows you to get the pond scum, but one of the responses from the earlier items caused a conflict. We had others report this a while back and have fixed it in the source code, so it will be fixed when we finish the update/patch we're currently working on.
Sorcerers can get into Tyr by just talking to Prospero in the magic shop though. He'll help you into the city via an alternate route.
