Necromancer in Taron mines??

[grumbly]

according to the walkthru I'm reading "At the first fork there's a Passage in the Wall that will take you to a necromancer that's holding some unicorns captive. Kill him and they'll join you. "

I cleared out the mines but I'm not seeing any necromancers? There was one glowing passage in the wall close to the entry to Lower Hadar and there was an undead enemy there with some necromancers but it wasn't an enemy hero and there weren't any unicorns there... just one might rune they were guarding.

where is this necromancer??