A woman whose mother was murdered when she was a child of twelve, is now, fifteen years later, working as a detective and still pursuing her mother’s killer, who, it turns out, is closer than she thinks.

i am just going to take the liberty: ?"when a detective receives a mysterious phone call, she dives back in the cold case of her's mother's murder."

Then shoot for a target maximum length of 30. While not the ideal, it's tolerable, permissible.

I think you have a concept for an interesting story, particularly the psychological impact off his discovery at a vulnerable age. He may be a geek, intellectually advanced for his years, but emotionally he's still only a 10-year old boy. In the gap therein lies an interesting subjective story line to complement and deepen the main story line.

Then shoot for a target maximum length of 30. While not the ideal, it's tolerable, permissible.

I think you have a concept for an interesting story, particularly the psychological impact off his discovery at a vulnerable age. He may be a geek, intellectually advanced for his years, but emotionally he's still only a 10-year old boy. In the gap therein lies an interesting subjective story line to complement and deepen the main story line.