Into the Dark Dimension. Great splash page to introduce this three-issue story.
In past issues, Clea has been shown living in the Dark Dimension, and in these issues she gets the residents of that world (including the Mindless Ones) to rise up and unseat its evil ruler, Umar—who is the sister of Dormammu, who was banished many issues ago. By the end, Clea is the new ruler of the Dark Dimension.
The world of Dr. Strange is very inside baseball. It has minimal impact on the rest of the Marvel Universe, and it can get very arcane (pun intended) and specific.
These issues give an extensive backstory for Dormammu and Umar that only the most diehard mystic arts readers will care about. It’s a perfectly good story—Roger Stern is a great writer—it’s just not one that most people will remember.
And look at how Paul Smith draws the mindless ones.
They never looked better.