A young, hot-headed loner must embark on a dark, twisted odyssey in Miami to rescue his sister from being forced into prostitution by mysterious kidnappers.

I agree with Richiev's reply and subsequent post.

All of my questions should have been answered by the logline. If you're sending loglines to a producer, you won't get the opportunity to answer these questions in a follow-up. Chances are, if there are questions like these, the producer would just move onto the next.

This is another attempt at an example logline.

I saw more of an explanation of the story from Gemini in his response to Mike, so this one should be better, (But I am taking some liberties as well, so this might not work exactly)
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"After his sister is taken, a devout youth pastor is forced by the kidnappers to rob his own megachurch in return for her release."
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As you can see I changed the character from hothead to a character who would never commit a crime. That way when the kidnappers force him to commit a crime it won't just a legal dilemma but a moral dilemma as well.

Not only that, the megachurch brings in millions every Sunday, so there is a method to their madness. The youth pastor has special knowledge of the layout. That is why he was targeted specifically.

Now he must commit this crime or his sister will be killed.

The twist might be, the leader of the kidnappers was wronged by the church, or another twist, perhaps his sister was the ringleader.

Hope this gives you some ideas for the logline.

2. He must go through the kidnappers’ tests of theft and violence in order to get her back.
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Well there you go Gemini, There's your hook and you didn't put it in your logline.

In order to rescue his sister from the kidnappers, he must commit a crime. (Or a series of crimes)

That is the hook of the story! (Meaning, it needs to be in the logline)

Because of the hook, your lead shouldn't be a 'hothead' but a 'law-abiding citizen'. Someone who would never commit a crime, (Like a pastor) but maybe have special knowledge.

1. The protagonist is 25 years old.
2. He must go through the kidnappers' tests of theft and violence in order to get her back.
3. The protagonist's sister is 27 years old; I'm still trying to figure out how the kidnapping element can work.

You use a lot of extra words in your logline.
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"When his sister is kidnapped a hothead must rescue her before she's forced into prostitution."

I think there's an interesting premise here but I have a couple of comments:

"young" - how young? Young could be 6, could be 16, could even be 26. Loglines (most of the time) thrive on specificity.

"dark, twisted odyssey" - same comment as above - specifically, what happens? Think visually, what will we see on screen?

"Miami" - I don't think we need a location. The plot remains identical if this was replaced with New York, LA, London, Sydney, Tokyo... etc. Only include a location if, without it, the logline makes no sense.

Final point (and this one is a bit more problematic) - His sister has been kidnapped (I think it's important we know how old she is too but we can probably get something from his age)... how does the protagonist know that she's being forced into prostitution?? It's not the sort of thing you'd find out about until she was found.

Instead, consider that his sister has fallen into the wrong crowd her boyfriend/pimp is forcing her into prostitution and never lets her leave. This makes sense and gets around the problematic kidnapping element.

Food for thought. Interested to see where it goes.

Hope it helps.