In the year 2000 of the history of the cosmos, representatives from the many different planets in the galaxy established a congress called the Galactic Federation, and an age of prosperity began. A successful exchange of cultures and civilization resulted, and thousands of interstellar spaceships ferried back and forth between planets. But space pirates also appeared to attack the spaceships.
The Federation Bureau created the Galactic Federation Police, but the pirates' attacks were powerful and it was not easy to catch them in the vastness of space. The Federation Bureau and the Federation Police called together warriors known for their great courage and sent them to do battle with the pirates. These great warriors were called "space hunters." They received large rewards when they captured pirates, and made their living as space bounty hunters.
It is now year 20X5 of the history of the cosmos, and something terrible has happened. Space pirates have attacked a deep-space research spaceship and seized a capsule containing an unknown life-form that had just been discovered on Planet SR388. This life-form is in a state of suspended animation, but can be reactivated and will multiply when exposed to beta rays for 24 hours. It is suspected that the entire civilization of Planet SR388 was destroyed by some unknown person or thing, and there is a strong possibility that the life-form just discovered was the cause of the planet's destruction. To carelessly let it multiply would be extremely dangerous. The Federation researchers had named it "Metroid" and were bringing it back to Earth-- when it was stolen by the space pirates!
If Metroid is multiplied by the space pirates and then used as a weapon, the entire galactic civilization will be destroyed. After a desperate search, the Federation Police have at last found the pirates' headquarters, the fortress planet Zebes, and launched a general attack. But the pirates' resistance is strong, and the Police have been unable to take the planet. Meanwhile, in a room hidden deep within the center of the fortress, the preparations for multiplying the Metroid are progressing steadily.
As a last resort, the Federation Police have decided on this strategy: to send a space hunter to penetrate the center of the fortress and destroy Mother Brain. The space hunter chosen for this mission is Samus Aran. He is the greatest of all the space hunters and has successfully completed numerous missions that everybody thought were absolutely impossible. He is a cyborg: his entire body has been surgically strengthened with robotics, giving him superpowers. Even the space pirates fear his space suit, which can absorb any enemy's power. But his true form is shrouded in mystery.
The planet Zebes is a natural fortress. Its sides are covered with a special kind of stone, and its interior is a complicated maze. On top of that, the pirates have planted devices and booby traps in the maze, and the pirates' eery [sic] followers lie in wait around every corner. Samus has now succeeded in penetrating Zebes. But time is running out. Will he be able to destroy the Metroid and save the galaxy?