The Go-Between (2015) online

In 1900 12 year old Leo Colston spends a blisteringly hot summer with the wealthy family of class-mate Marcus Maudsley at their Norfolk estate. When Marcus falls ill Leo is befriended by the daughter of the house, the glamorous, captivating Marian, who is to be engaged to disfigured Boer War veteran, the kindly Hugh Trimingham. Totally smitten by her, Leo agrees to carry business letters between herself and young tenant farmer Ted Burgess. However the messages are not what they first appear to be and will have unfortunate consequences spanning half a century when Leo meets up with Marian again.