She's either dying or bored to death
Franco himself stars as Mathis Vogel, a defrocked priest who writes to an pseudo S&M magazine about demonic activities and black magic practices. One night, he goes to an erotic show based around a Black Mass, and lo and behold, he thinks the whole thing is real and that everyone is possessed, he goes on a killing spree, with the likes of a model named Anne (Franco regular Lina Romay) being a prime target.
That's about it as far as plot is concerned. There's potential here for some interesting social commentary, but Franco doesn't seem to be too interested in that sort of thing. He seems to be more interested in sex and female nudity than saying anything relevant. To be fair, Romay does a fine job, the aforementioned nudity is sometimes pleasing to the eyes and there is a great bit of shocking violence, but after a while "Exorcism" starts to get really boring. Most of the violence isn't all that graphic, and Franco isn't really the best director. Sure, there are one or two nice shots, but the direction is kinda lifeless, with way too many lingering shots and repetition to really get invested.
Oh look, something shiny!
Which leads me to my biggest complaint: this movie is fucking boring. Franco seems to be obsessed with showing you the same thing (Black Mass rituals and writhing naked bodies) to the point of making the whole endeavor redundant to sit through. This is a movie that's main goal is showing off as much boobs, butts, bush and sleaze as possible, but it never feels erotic. It's all shot in a really matter-of-fact style, and after a while all of the events end up blurring together. You can only show sleaze for so long until it loses it's impact and becomes uneventful.
I know, there's an audience for this. For that audience (and fans of the directors work), you'll probably eat this up. Me? I just kept wanting to hit the fast forward button.