Murder at Twilight — Fleur Hitchcock

When Viv has a fight with Noah, she doesn't think it'll be the last time she sees him. But when she gets back from school, he's nowhere to be found and there are police cars everywhere, lights flashing and sirens blaring.

Viv is sure Noah's run away to get attention. But it's really cold, and getting dark, and the rain just won't stop falling. So she sets off to look for him, furious at his selfishness, as the floodwaters rise. And then she finds him, and realizes that a much more dangerous story is unfolding around them...