The Stranger or The Outsider (L’Étranger) is a novel by Albert Camus published in 1942. Its theme and outlook are often cited as examples of existentialism, though Camus did not consider himself an existentialist; in fact, its content explores various philosophical schools of thought, including (most prominently and specifically) absurdism, as well as determinism, nihilism, naturalism, and stoicism.
Most of us have read The Stranger in high school. If you did not, I suggest you read this immediately. It goes by in a flash and it a classic story of an existential character who finds himself on trial for murder and condemned for his detached and nihilistic manner.