A woman stands up one man for another because he is nicer, so she thought. She soon discovers he’s a serial killer and her life depends on the first man to send that psycho to hell.
This is a tough one. You should probably start with the serial killer angle. “When she discovers her date is a serial killer…” then go to the fact she must receive help from the man she stood up.
However, that being said, lead characters are proactive, they solve their own problems. You might want to write this from the point of view of the man who was stood up. He is the one saving the day and taking action.
Agree with Richiev.
You gotta decide who owns the story. The woman who foolishly stands up the nice guy in favor of the wrong guy only to realize.. ? Or the nice guy who maybe was too nice, who has to rise to the occasion and become a mensch instead of a milquetoast (character arc) in order to rescue the damsel in distress who stood him up?
Whoever owns the story — which is to say, the one with the stronger character arc — frame and focus the logline around that character as the protagonist.