On my way to Busan…

Two individuals are inside a train, one in a white shirt and denim shorts is bent over, while the other in a blue shirt stands nearby; the scene cuts to a man in a dark jacket turning his head, then to a person in a white uniform walking down a train aisle, followed by a man in a black jacket grabbing another person in a white shirt, and finally a close-up of a hand with blood on it.