When a deranged brother suddenly kidnaps his younger teenage sister, she must decide whether to awaken or resist her own sadistic urges to survive without becoming a killer herself.
Because of how short loglines are, it helps to stick to the perspective of one character.
“When she is kidnapped by her brother, a terrified girl must…”
I am unclear what she must do; in your logline she must make a choice but the story would be what she does after that choice.
You’re right. The second half of the logline can be confusing especially now that I’ve reread it a couple of times. Basically, the sister has the potential to become a serial killer in the making but she does her best to suppress these urges. However, when her unstable brother returns (having been estranged from the family years ago) and kidnaps her, she begins to realize that she might die. This is where the conflict arises in her decision to channel her violent tendencies as a way to escape (kill her brother) but could result in her enjoying it too much and going down the same dark path as him. The whole slippery slope dilemma.
Here’s an edit but still unsure:
When she is kidnapped by her brother, a young girl decides to use her own sadistic urges to her advantage to turn the tables on him and escape.
‘After escaping her abduction, a terrified girl makes up her mind to find the abductor and quench her sadistic urges.’
What if you keep the abductor a secret. This can be so good, as his brother is the kidnapper and she has decided to inflict pain upon his abductor.
You made it thriller. What if you turn it into comedy:
‘After escaping her abduction, an annoyed girl gathers balls to find the abductor and quench her sadistic urges.’
It will be so funny, as her long quest with sadistic urges would end up on her brother and now she must fight her urges.