The crisis that sparked it all, during the Cold War. In the era of the Cold War, Naked Snake—later known as "BIG BOSS"—heads to the Soviet Union to assist in the defection of scientist Sokolov. However, due to the betrayal of Snake's mentor, a soldier known as "The Boss," who is also called the mother of special forces, the mission fails. Sokolov is taken away by GRU Colonel Volgin. One week later, Snake is ordered to rescue Sokolov and assassinate The Boss, and he returns to the Soviet Union. Within the ever-changing "SCENE" of the times, the mission that will become the origin of a legend is carried out. A grand epic that revolves around the birth of the hero "BIG BOSS," the origin of the Metal Gear saga.