Hiro, a 20-year-old Japanese student, sits next to an old man on a train to Berlin. By mistake they exchange phones and read each other's text messages. Hiro believes that the man's messages show that he is going to Berlin to kill someone. Hiro's first day in the city is a race against time as he tries to warn people of an assassination plot. But is the plot real or does it exist only in Hiro's imagination?