Like Bledavik, this city has its own overhead map. Enter from the SOUTHERN marker. Head NORTH. The shop at the top of the stairs sells items and accessories and has a save point. Of note is the Ether Doubler, which doubles EP cost and doubles ether strength. This will be VERY useful later on in the game, but it is unlikely that you have 38000G lying around to buy it now. There's also a man from the Yggdrasil who will sell you Gear parts.
Head out the NORTH exit to the cathedral. After the cutscene, follow Margie to the NORTHEAST. Go up the stairs for another cutscene. Keep following Margie up the stairs again. After a deja vu moment, head back to town. Head to the SOUTH and Maison will appear. Talk to him, and then go inside and talk to Sigurd. After receiving lots of information, leave the house and head NORTHWEST to the bridge where Bart is. Talk to him for another cutscene. At this point, go to the town hall across from the shop for the upcoming battle plan. After, head to the shop and upgrade your Gears. Talk to Bart when you're ready to leave. The time has come to take back Aveh.