The resourceful best friend and panicked boyfriend of a young girl in suburbia struggle to overcome a shady drug dealer, and the cops, in order to defeat the satanic forces possessing her.

I like that. Thanks!

I was thinking the opposite, I believe the Drug dealer is trying to saver her, maybe in love. The lead character doesn't know that and believes the Drug dealer is after the her friend to harm her. (A misunderstanding)

In the end it's the Drug dealers info that saves the GHB possessed character.

Ok. I see two options:

1) It's a crime story and the twist is that it's not a drug overdose, it's out right demon possession, as you say.

2) It's horror/occult. What's at stake is her soul. The main character's goal is to save her best friend's soul. Then, we get the first twist at the end of act two: It appears she's not possessed but has been the victim of a lethal dose of GHB. The priest is sent away, her symptoms lessen, and she goes to the hospital for treatment. But drug tests reveal that she has clean blood. Then, the demon returns for a final battle at the end of act three.

Whether it's soul or mortal life, the main character's goal is to save her best friend, because that's what friends are for. Do you think it requires something more concrete?

Thank you, Richie. That is a very helpful reworking. Just one question. You phrase it as "a determined drug dealer." This is a plot point I had not considered. Were you thinking that he's determined to not be incriminated? Or maybe he tried to kill the girl with the overdose but she got away and now he's tracking her to finish the job? Of course, these are story questions that I as the writer have to work out. But I'm curious what you were thinking when you wrote the word "determined."

If it's a bait and switch story, I think that outright demon possession is the stronger Big Final Reveal. To find out she's 'only' suffering from a drug overdose would be a let down.

But I'm still confused.

Be careful with "surprise twist" endings. They seldom work, unless you're a master at it (like 'The Sixth Sense'); more often, they're predictable and so much emphasis is placed on the "twist" that character development and plot believability go out the window.