A rookie female detective, out to prove herself, is tasked with protecting a single mother and her son when a serial killer learns that the young boy claims to be the re-incarnation of one of his victims, and tries to kill him again.

Loads of pronouns and antecedents here, too long, too confusing, provokes too many questions for clarity…has to be simplified. And too much plot for a logline. Keep it simple: protagonist, antagonist, conflict, stakes, with a single adjective here and there to define character, like “rookie detective.” We don’t need to know she’s female, and you don’t need to add she’s out to prove herself; is that not already implied? Aren’t all rookies out to prove themselves? And if she’s a detective, why is she assigned to protect them? Shouldn’t she be out detecting the suspect?

Don’t get bogged down in supplying as much information as possible; tell us only what we need to know to understand the story and make it interesting. We don’t need to know about the single mother, just the kid. Save the fleshing out for a synopsis or even just the script.

A rookie cop must protect a young boy being targeted by a serial killer after the boy claims to be the reincarnation of a previous victim.

The idea is to get people to want to read more, so just give us the basics and make it compelling. Even this example, though short enough and to the point, still raises the question of why a rookie has such an important task, but that question is asked because one wants to know more about the story, not merely to comprehend it. And as long as the more detailed materials outlining the story make these things clear, it can all work.