“Every day, I come by your house and I pick you up.

[Snoopy]

Let The Right One In. It's a good film but there's a LOT missing. Characters, plots, relationships. Even timelines are messed around with. I know adaptations often have to cut things but there's a bunch of important events that are either glossed over or not in the film. I'd say watch the film first, then read the book.