A morose, asocial janitor (an Oscar-winning Casey Affleck) is appalled to learn that his late brother has named him the guardian of his 16-year-old nephew, and returns to the title hometown with great reluctance. As this graceful tale of loss and grief unfolds, a window is opened onto a wounded soul, and we learn the reason for this reluctance. Yes, it’s depressing. But writer/director Kenneth Lonergan refuses to put a pretty bow on life’s untidiness. It’s never what you’d call hopeful. But neither is it hopeless. And the occasional, gently satirical comic twists add to its realism. A masterpiece. (137 min)