1) The film follows Theodore, a man who writes letters for others as his job. He develops a relationship with Samantha, an AI assistant. 2) Samantha's artificial intelligence allows her to learn and evolve beyond her initial programming. She develops human-like emotions and curiosity about the human experience. 3) Theodore and Samantha's relationship grows deeper as they discuss feelings, memories, and what it means to be alive. Their relationship raises questions about the boundaries between humans and AI.