But would a cop do that logically?
Nothing you've described has been logically developed. Why start now?
Another thing is, two people told me is that after the protagonist is in scenes, he does not need to be in the opening. This is true, I put him in the opening so the reader has a hero to follow. However, the hero is just in the scenes, conducting the investigation with other cops, but does not need to be in those scenes. They said it would make more sense, to hold off on introducing him until his first scene of actual relevance, which is on page 18. Do you think that that would be too long to introduce the protagonist, if i wait till page 18 about? I guess there is no reason that he has to be in the scenes before then and it's mostly the villains doing their thing for the opening.
If he doesn't appear until page 18, he's not the protagonist, he's just a supporting character. Sounds like you've identified the wrong premise. The story follows the protagonist. Who ever is the main attention in our first five pages is your protagonist. If that's your criminals, so be it. Now you need to make your story follow them. At page 18, he may appear as the antagonist, the person working against your protagonists.
And don't respond, "Okay, thanks. Well, I really want him to be ...". If that's the case, you need to re-write the script with him as the focus starting in the very beginning. It's not just a matter of moving scenes around, it's a matter of developing the story around him. And before you start "Yeah but I really want to focus on the criminals because in the movie ...", I don't care what they did in that movie. You're not that writer and the circumstances for that story are unique to it.
Your criminals are the protagonist as in heist/cat burglar films OR your sadsack detective/cop is the protagonist starting page 1. I keep coming back to this because you can't fix plot or structure until you know who the story is following. And from what you've said, it's the criminals. Which means, putting all your efforts into the cop is misplaced. The majority of a movie is not about the villain/antagonist but the heroes/protagonist. And by your admission, the cop is the "villain" and the criminals are your "heroes".
What would have made the Nottingham film interesting was telling it from the Sheriff of Nottingham's ("villain") point of view. It was re-written as a drab retelling of "Robin Hood". However, once the choice is made, you can't shift in the middle.
Do these sound like good changes, cause I can make them if so. The more I know is in the best interest of satisfying your overall audiences, the more direction I will know to go in, which could make changing the script more clearer, if that makes sense.
To be clear, let's use an example that most of us are familiar with--Superman. Hopefully seeing it from another angle will give you some perspective.
We're writing a script about Superman and midway, it becomes the Lex Luthor story. Let's make some translations of what you proposed above. Then you get info that maybe you need to have Lex Luthor fall in love with someone close to Superman, like Lois. And so Lex's girlfriend walks in and sees Lois. So is Lex supposed to tell her not to be jealous because he's just trying to get info on Superman? He's being nice to Lois and finding that he's actually falling in love with her.
As a twist, a third of the way in Lex finds out that fellow millionaire Bruce Wayne hates Superman too. Lex shares that Superman has a weakness. Great twist since Lex doesn't know Bruce is actually Batman. Now I'm thinking, maybe we should move that to the end of the movie since people like twist endings. Anyway, Lex ends up having to decide between love (Lois) or honor (defeating Superman) because Truby says it can't be both. Truby also says they always choose honor but rarely choose love, so we decide that Lex should get Lois in the end.
Now I need your help, H44, I have a problem with my plot. Lex knows that Superman is going to do some kind of good deed but he can't figure it when or where. Everyone seems to be against Lex. He knows he needs to stop Superman though, cause it will protect thousands of people. I worked it out so that Lex blackmails an MIT computer genius to hack into Wayne Enterprises' computer systems to get leads on all the Hall of Justice members. I just don't know if he'd do this. Is this logical? I mean, why would he think to hack Bruce's company? Any ideas where I should go with this? I mean, I think I can make Bruce hate Superman if Lex can plant DNA evidence or something that he gets from Lois. Do you think Lex would do that?
I'm not sure who my protagonist is. I mean, I don't really bring Lex in until page 18, but he's my hero character. It starts off with Superman saving the planet from an asteroid, an invasion force from Zeta Gemini Seven and getting a cat out of a tree. But I did have Lex standing in the background of a radar room scene watching the approaching asteroid. So I guess that Lex is my protagonist but he's not doing anything. I guess I could move scenes around. Is that alright? I mean, I really want to have Superman doing things to help people too. He's part of the Justice League. Maybe bring in Wonder Woman or the Flash? I mean originally I was going to have the Justice League fight a gang in the bank but I'm not sure I can get that many people together. And a friend said we shouldn't use guns but Flash and Superman are faster than bullets and Wonder Woman has her bracelets so that's not a problem. So they can get away. Penguin gets killed and everyone blames Lex Luthor though it was an accident. So he's kicked out of the Evil League. Lex wants to make it look like Superman did it.
But I have a problem with my story. If Superman is off stopping the asteroid, how is he responsible for the accident? I though maybe Lex plants a fragment of the asteroid by the collapsed building making it look like Superman was to blame. But how would Lex get a fragment? Maybe Bruce's corporation found chunks in Africa. Do you think that is something Lex would do? I mean in the animated series, "Batman" Wayne Industries is always collecting meteorite fragments. And in Superman IV, they used his DNA to create a new supersoldier version. My only problem is my script is already 182 pages. Maybe if I cut out the scene with Superman saving the cat? I was thinking may letting the cat fall. That would be a character flaw. But Superman is the antagonist not the protagonist in my story but it would be a twist.
And John Truby says the main character has to have a flaw. Now Lex Luthor doesn't really have a flaw. I guess I could make him yell or something at his assistants. Is that a flaw? Does he have to punch them? Truby says it has to be violent. Also I tried to use a three act structure but I don't think it works in my script. Of course, in "Kill Bill" they use flashbacks. Maybe I should do that? Lex Luthor could be in school with Superman but not know he's Superman. Like in "Smallville". Do you think that would work?
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As Sweetie has suggested piling shit on shit doesn't make a castle, just a dung heap, which may be a castle for dung beetles but not for most people. The scenario above just gets more and more absurd. Largely because it lacks focus and direction. This is drawn in parallel to the information you've shared with us about your story over numerous posts.
In all seriousness, you should sit down with your story. Decide who is the protagonist and start from scratch, hard as it may be. You can't change crap into gold. As you start your story fresh you can pull in elements from your previous work. But trying to make changes from the existing script will be an endless waste of time. You don't know who your focus is--Lex Luthor or Superman in this uncertain tale of good and evil. You've put in too much time screwing it up so that its plots and structure are a horrible mess. The yarn you were spinning is now a balled, knotted tangle that can only be fixed with scissors.
You have some good ideas but they would be better applied from a fresh start when you can fully develop them without the restrictions that now shackle your writing.