After getting a clue from Alanna's nursery rhyme about the Right Knight, you should head northwest to Doomingdale Forest.
Go to Doomingdale Forest to reach Brigadoom
Go northwest from the town of Zere to reach Doomingdale Forest. There are poisonous ponds in the area, so try to avoid them.
As you go toward Brigadoom, you might encounter a stairway that is blocked by some poisonous water. You can avoid stepping through that if you go to the east and up some stairs.
Once you reach Brigadoom, you will find the Wight Knight there. After he talks to you, you can explore Brigadoom. There are red and blue chests around the area, so be on the lookout for those.
Eventually you will reach a throne room. Once you do, the Wight Knight will appear, and so will Morag. After some things happen, you will have to fight Morag. Talk to her to start the battle.
Morag knows some magic, like Crack, and she also has an ability to dance. Mostly, she will just hit you with her knife. It should not be too difficult to defeat her.
Return to Stornway
Talk to the Wight Knight after Morag is dead, and some things will happen. Then you should exit from the underground area and return to Stornway. Be sure to go outside before using a Chimaera Wing. It will only work if you are outside. You can use the Evac spell to get outside. Don't worry about conserving Chimaera Wings. They are cheap and you can buy them in the Zere shop and probably others.
Back in Stornway, go talk to the King, and he will unlock the treasure room for you. Go up the stairs behind the throne and go east to the treasure room to get various things.
Be sure to visit the Inn before you leave. Erinn found an alchemy pot. Being a Celestrian, you can talk to it. It calls itself Krak Pot. It's pretty easy to use. Just put the cursor next to a recipe, and the needed ingredients will be listed in the top screen. If you have the ingredients, you can create the thing in the recipe. You can find recipes all over the world, so be sure to talk to everybody and check every bookshelf.
Now that you can use Krak Pot, you will find Bill standing near the signpost in the center of town. He has a mission asking you to make a Panacea. He will give you the recipe.
The king has opened the gate that is in the northwest part of the Stornway region, so you should go there next. The gate leads to Coffinwell.