To the North East of Seaside is a small desert. The enemies are very difficult so be prepared.
You'll see a little hut in the desert. Go inside.
You'll find a Fire scroll in a chest inside. You will need it to burn the giant log North of Seaside. That's where you'll find your son, the other missing boy, and the final boss.
You might need up to 50 Cure 3's, Level 19 and the Milk to beat the warlock. First you need to beat 6 Minion's he spawns.
And that's all she wrote.
