In a suburb of Stockholm, a friendless young boy named Oskar is constantly tormented at school and imagines revenge fantasies in the courtyard outside his apartment. It’s there he meets Eli, a peculiar (seemingly young) girl who’s just moved in next door. She makes little effort to hide that fact that she’s a vampire (to him at least), and while innocent Oskar is slow to catch on, he’s smitten with her nonetheless.
Learning of his hazing at school she encourages him to fight back; which he later does. As they talk and become closer, her “father”, an older (still human) travelling companion who provides for her fresh blood (draining it from murder victims), gets caught in the act, forcing Eli to kill him.
With her human counterpart gone, Eli gets desperate and starts feeding off of the residents of the apartment complex, attracting attention and danger. After a suspicious and vengeful neighbor figures out what she is and tries to kill her (she kills him, with Oskar’s help), Eli decides to leave and kisses a heart broken Oskar goodbye.
Left alone at the public pool, Oskar is again confronted by the sadistic bullies, this time threatening to cut out his eye. Eli arrives and saves him --killing all of the bullies. Happy to see her, Oskar ignores the blood and body parts strewn about and just smiles at her like a boy in love.
The film ends with two riding on a train with Eli in the crate by his seat. They exchange words by tapping Morse code on the side of the box. Oskar is her new travelling companion.