Solid Snake has been dropped in Outer Heaven, a small country that is heavily armed , and that has become very active. Secret imformation about a walking battletank armed with nuclear weapons was acquired.
NATO had immediately sent his best agent, Grey Fox, but he had vanished without a trail. Right before his disappearance he had sent one last message: ...Metal Gear... Now NATO was forced to send its youngest agent, Solid Snake.
Solid Snake rescues Grey Fox. He tells Snake that in the heart of Outer Heaven there is a heavily guarded tank called Metal Gear,that is armed with nuclear weapons.
Now you, Solid Snake, must continue to infiltrate Outer Heaven, and find Metal Gear and destroy it.