After his private military force, Militaires Sans Frontières, is destroyed in Ground Zeroes, Big Boss falls into a nine-year coma. Upon waking in 1984, he takes the codename "Venom Snake" and leads a new mercenary group, the Diamond Dogs, to seek revenge against those responsible. His mission leads him to Afghanistan and the Angola–Zaire border, where he hunts down the culprits and confronts a world filled with mercenaries and warriors robbed of their past and future.