Die Hard 4, also known as Live Free or Die Hard, is the fourth installment in the Die Hard film series. The movie takes place in a post-9/11 world where terrorism has evolved to target critical infrastructure. The story follows John McClane (Bruce Willis) as he tries to stop a cyber-terrorist attack on the United States. The film features a star-studded cast, including Timothy Olyphant, Maggie Gyllenhaal, and Justin Long.