Walkthrough tips, Campaign discussion [Heroes 5: Hammers of Fate].

I apologize for bothering you, but I have a problem with Campaign 1, Mission 5.
I made it through the "Gate Garrison" (where Duncan is) with what I had;
But I can't reach "Gustav's Bend." After about two days, a red enemy appears there, and even if I run away, he chases me as if he has the entire map revealed. I've tried training. I even changed the difficulty to recruit!
PLEASE HELP!

Here's what I did: I took the Dwarf Castle and everything around it, went down into the underground, and reached the first Human Castle. I fully upgraded the Dwarf Castle (for money), took the Human Castle with almost no losses, immediately built training halls, and turned all peasants into archers. I started taking mines in the area, and I found a magic house that unlocks the Mage's Guild, showing all the castles. After 2-3 weeks, the red enemy appeared. I fought him in an open area and defeated him with almost no losses. Then I went to find Duncan, capturing mines along the way. I rescued him, saw the garrison to Gustav, and was almost shocked... I turned to the castle on the right, took it, although with significant losses (by the way, everything was built there, even angels). Then I gathered an army, which turned out to be quite strong from all the castles. I sold all the resources, and there were 100-200 of each, and with that money, I trained and upgraded archers. I went to the garrison, and in the army, the main force was paladins (about 60) and crossbowmen (about 1000). I divided the crossbowmen into two slots because they could kill everyone with one shot anyway. I easily took the castle and destroyed the enemy "fleet" without losses. That's it =)


Now, about myself: I cleared both garrisons in the last mission, but I can't storm the Dwarf Castle, no matter what I do. I'm tired of replaying. If anyone has the time, please tell me how it ends (the plot of the very last cutscene)