Evelyn's lab is on the beach on the West/top left screen direction, close to the rogues who have the mayor's staff. Your characters say something about the lab once you get in the area so that you know you have to use the reveal scroll. I think I got there by exiting town by the north entrance then moving west, I'm not at home for a week so I'm afraid I can't give more precise directions.
About the puzzle rooms loot, for me there was some sort of water door preventing me from accessing it.
