This story was written because Erik Larsen had lost his home in Oakland due to a fire. There was trouble in publishing the 'Revenge of the Sinister Six' storyline on time, so part two was split into two separate issues. The first part being the main story and the second being the two-part 'Diabolique!' story. These were issues #19 and 20 of Spider-Man.
This will be brief since most back-up stories are due to late comics or anniversary issues. They recap the main character's history or focus on one of his or her secondary characters, to give that person some needed background.
Terry Kavanagh and Scott McDaniel actually provide a decent story here. It involves Peter Parker doing a job for the Bugle at a new museum exhibit which focuses on 'The Diabolique Cask'. MJ is there at the premiere with Peter and the two have some nice, couple moments. Obviously, the scientist in Peter assumes that there is more to this than everyone assumes and investigates as Spider-Man. Spidey is searching the museum as nearby statues come to life. They attack the hero while the diabolique cask brings something new to life.
Not bad for a back-up story at all. I'm sure Kavanagh and McDaniel had little time to prepare this, so they are due some credit. Spider-Man vs. Diablo is an interesting idea.
Can't ask for much more here than entertainment, and the story delivers on that.