The Go-Between, by L. P. Hartley
The first line will be familiar to all: The past is a foreign country; they do things differently there.
Leo, now well into his 50s, opens up a box of memories and tells the story of the summer of 1900, when he turned 13. It was first a sort of awakening, and then a life-changing trauma. As Leo remembers his lost innocence, he also wonders whatever became of the people involved...
Leo goes to stay at a country house with a much wealthier school friend, and since Marcus' older sister is engaged to the local baronet, there is a constant social whirl around her. She enlists Leo as a messenger in her secret romance, and it all ends in disaster.
This is a really famous novel, considered a classic of the 20th century, but it mostly did not enchant me. Its exploration of the emotional and mental life of a young teen boy did not reel me in. It was fine, but I did not love it, and I was ready to be done well before it was over. My final opinion is meh. Sorry, L. B. Hartley.