When 12-year-old Elsi Björkman and her mother Paula return from a week's holiday abroad, Elsi immediately notices that someone has been in her room. She tells her mother about it, but she does not believe her. At the local supermarket Elsi meets Henry, who seems to spend his time returning shopping trolleys. Elsi does not know anything about the boy, who has an irritating habit of appearing from out of nowhere, only to disappear again, as if into thin air. Nevertheless, the children become friends.