Engineer Chen Yan, rated C and given no year-end bonus, submits his resignation letter and completes the handover down to the very last page, leaving behind three risks that nobody takes seriously. After he leaves, his former employer replaces components to save 41 yuan, secretly alters the temperature controls, and deploys the wrong patch. As a result, 220,000 robot vacuum cleaners begin malfunctioning one after another, followed by mass recalls and a stock trading suspension. The company even turns around and sends him a lawyer's letter accusing him of leaking trade secrets. One submission record finally reveals the truth. At his new company, he builds a machine that can recognize its own replacement parts, and gives the testing team the right to say no.