Upon entering the estate, the undead army split up to quickly find the mage lord (I don't remember the name). However, they encountered resistance consisting of mages and city soldiers. But even they couldn't prevent the necromancers from finding the mage and killing him. After his death, a secret door opened, and our heroes headed there...
Screenshot #1
We just entered the first rooms.
Screenshot #2
Searching.
Screenshot #3
Finally found him.
P.S. I finally managed to level up the zombie; now he's a soulless level 1 creature (before that, he was level 0, haha). It's a pity that he can't be upgraded further; he'll just run around uselessly... although, if he kills an enemy, he turns it into a new zombie. Weak meat can also be useful.