Talk to Kofu at the Magic Guild, and agree to help him. The second item on the menu outside Shanoah will now take you to Davis' house at Masaki Head. Note that you can only cross the causeway to his house during the daytime. Night will fall a short way into the scenario, so make sure you're ready before you set out.
Head right towards the house. The door is locked, so continue right. Chat with the boy, then head back round to the front: Davis should be back. He'll invite you in. After a conversation, his son will call him out, and you'll regain control. There's a save point in the back room if you want to use one. Leave the house and head round to the back. There's a door where the boy and the dog were earlier; go inside. Talk to them, then head back to the house and go to bed.
In the morning, talk to Davis. Then head round to the barn and talk to Ed. Go back to Davis and talk again. When the music changes, head back round to the barn and talk again. Now head back to the causeway. Examine the highest point. The hawk will deposit a bottle in the water to your left, which contains a letter from Kofu. Read it.
Now when you return, Ed should be missing from the barn. Go back to Davis, examine the shelves behind him until you've read the scrolls, and talk to him about them. Head to the back of the barn. Remove the plank from the bottom of the wall behind the spot where Karon was lying, then examine the floor in front of it for a loose plank. Remove that too, and slide the plank to the right of it across into the gap to reveal a ladder. Go down.
At the bottom, you can go either left or right. If you go left, you'll come out in a pit behind the house; there's nothing to do here yet, and you might be attacked by Zombies, which will slaughter you unless you run. So go right instead. You'll come to a mazelike cave; there are Oak Jellies in here, but those should be no problem. There are two exits at the top of the screen. The one to the right is a dead end for the moment, since you can't open the door. You need to know that, though, so head up that way and check the door and the handle (to the left of it). Now go back round to the opening to the left, and go through the door. You'll be in a large rectangular room. There's a corpse in the top right corner. Make sure your HP is full, because when you've examined it a few times, the Eleanor Zombie will attack. She's not as tough as the normal Zombies ("waes se gryre laessa / efna swa micle swa bith maegtha craeft / wiggryre wifes be waepnedmen..."), but she uses magic - Wolfstorm, Icefall, and Earth Heal.
Now head to the ladder, climb back up, and go round to the front of the house. When Ed leaves, follow him. Go to the room to the right of that in which you fought Eleanor. Ed will open the door. Inside is that "Gate of the Dead" of which Kofu's letter spoke. Read the note on the floor, and talk to Ed. He'll try to remove the Magic Stone from the wall, but fail; so it's up to you. Check the stone again, talk to Ed again, and so forth. When you realise water is necessary, return to the barn and collect a bucket from the top right, then head to the causeway and fill it. Go back to the Gate of the Dead and try it with the Magic Stone. Things will get rather exciting.
After everything calms down again and you receive your scenario experience, head back round behind the house; a new path will have opened, and you can enter the woods and get an Aqua Stone from the tomb. Then head back to the causeway. As soon as you cross the bridge, look for a sparkle at the bottom of the screen, below the point where you stood when the hawk appeared; that's the Shield Magic Stone, which you probably don't want to leave behind, so check it twice to take it.
Finally, be sure to check back with Kofu for some gold.