The Go-Between (1971)

Summer 1900: Queen Victoria's last, and the summer Leo (Dominic Guard) turns thirteen. He's the guest of Marcus (Richard Gibson), a wealthy classmate, at a grand house in rural Norfolk. Leo is befriended by Marian (Julie Christie), Marcus' twenty-something sister, a beauty about to be engaged to Hugh (Edward Fox), a viscount and good fellow. Marian buys Leo a forest-green suit, takes him on walks, and asks him to carry messages to and from their neighbor, Ted Burgess (Sir Alan Bates), a bit of a rake. Leo is soon dissembling, realizes he's betraying Hugh, but continues as the go-between nonetheless, asking adults naive questions about the attractions of men and women.