Islands of Secrets

So, I finished all the original campaigns and decided to play through the additional campaigns. I chose to play "Heart of the World." I selected the "Warrior" difficulty level (just in case there are some moments where it's very difficult to win on "Veteran"). I completed the first mission without any problems. In the second mission, I defeated the orcs and teleported to the other end of the map through a one-way portal. I explored that area and eventually captured the Tenebrad Castle. That's it! No matter how much I search, I can't find any way forward. The brown player is just wandering around, and he's not on the map... what should I do? It's like a dead end...