The middle of the "Phantom of the Sewers" opens with a flashback to Etrigan battling an evil wizard and his creatures in the middle ages, presumably at least partly to have an action scene with Etrigan since he appears as Jason Blood for most of the book, and also to establish some backstroy about what exactly happened to Etrigan/Blood between the fall of Camelot and modern times. A quick scene, but really fun looking, especially the two-page spread.
Back in the present, Jason has used the Philosopher's Stone (that's the Sorcerer's Stone for you Americans...) to freeze out the Etrigan side of his nature, but Glenda has been taken by the Phantom, a scarred actor named Farley Fairfax, who mistakes her for a woman who betrayed and cursed him years ago. Our heroes pursue, and Jason is able to turn back to Etrigan (first only half-transforming, which looks kind of funny) and arrives in time for the final confrontation.
Mike Royer inks the cover and 23-page story.