“Elia’s Quest” – “The Showdown” [Campaign 3, Mission 5]

This is a bug. The remaining three heroes should join immediately after the siege is lifted, regardless of the demon cities. In fact, the entire Dungeon faction (3 demon cities and one Dungeon city) is captured by Ilia with her starting army and Chaos units without any problems. Duncan and Isabel train troops for Frida, and Wulfsten's army is used as expendable, as he doesn't mind losing it. Frida, with a huge army, defeats the gnome. That's how it works on the hero level. The end.