In 1982 Stockholm, Oskar is 12 years old and lives in the suburbs of Blackberg with his mother. Eli is a vampire that has just moved next door. Since they look about the same age, they form a formidable friendship. At school, Oskar is bullied and Eli encourages him to fight back.
Eli needs to constantly feed on human blood, and Hakan facilitates that for him. One day, he fails to do so, which prompts Eli to seek out human blood for himself. He ends up killing his victim. Hakan disposes of the body, but not before somebody saw what Eli had done. Later, Hakan attempts to retrieve blood from a teenager but ends up disfiguring his face to avoid being identified by the authorities.
At the hospital, Hakan is willingly drained of blood by a starving Eli. After this, Eli and Oskar grow closer despite their sexual ambiguity. The relationship grows stronger and Oskar proposes a blood contract that will be sealed with a cut. Eli holds back his lust for blood and makes it through the covenant without harming Oskar. Later, Eli feeds on Virginia, who begins showcasing signs of becoming a vampire. Oskar later learns about Eli's vampirism.
Virginia engulfs after turning to a vampire and getting exposed to sunlight. Lacke, Virginia's boyfriend, seeks revenge but suffers the same fate as her girlfriend. Oskar finds a hard time coming to terms with Eli's killings. Back at school, the bullies hunt down Oskar and subject him to a number of torture tactics. Eli arrives in time and kills the bullies.
