Ethan Morgan is a geeky freshman, not trusted by his parents to stay home alone with his little sister Jane. They hire Erica, a girl from Ethan's high school who is a huge fan of "Dusk", as a babysitter. However, Erica comes across her best friend Sarah, and Jesse, Sarah's vampire ex-boyfriend, on the night she is to babysit, and decides to attend a party that Jesse is throwing instead. During a fight between Sarah and Jesse, Sarah ends up at Ethan's house and tells Ethan's parents that she was asked to babysit instead. Ethan has a vision when touching Sarah, and notices she has no reflection in the mirror, leaving him suspicious of her. He confides this in his dorky best friend, Benny. Sarah leaves to get Erica back from the party, knowing the party is full of bloodthirsty vampires. Curious, the boys have Benny's grandmother watch over Jane while they follow Sarah. They see her feed on a rat and realize she is a vampire.