Samus Aran, the most successful bounty hunter in the history of galactic civilization, has conquered the Space Pirates on their fortress world of Zebes and survived multiple encounters with the life-sucking Metroid parasites.
Not long after the Galactic Federation discovered the Metroids on planet SR388, a group of Space Pirates stole several Metroid specimens and planned to use them to fuel their assault on galactic civilization.
Samus' adventure began when she landed on Zebes, intent on destroying the Space Pirate's operations and eliminating their leader, Mother Brain.
After battling her way through the fortified planet, Samus located and ultimately defeated Mother Brain, but not before facing several hostile - and hungry - Metroids that nearly took her life.
Soon after this first major victory, the Federation deemed the Metroids too dangerous to exist and sent an elite group of soldiers to SR388 to exterminate the entire local Metroid population there. After contact was lost with the team sent to the planet, Samus was dispatched to finish a job suited to no other.
With difficulty, Samus excavated deep into the planet's crust and eradicated the Metroids hidden throughout the remote world. Surviving everything the local inhabitants threw her way, one target ultimately remained. The colossal Metroid Queen offered Samus a challenge she nearly couldn't match. With the massive beast felled and Samus' mission complete, one final surprise awaited.
A lone infant Metroid hatched before her eyes - the last of its kind. Confused and alone, the tiny lifeform developed an instant unbreakable bond to Samus as though she were its mother.
Unable to deliver a final blow to this infant and exterminate the Metroids, Samus instead delivered the creature to the nearby Ceres research station for intensive study.
Departing the station to seek new bounties, Samus quickly received a desperate distress signal urging her to return. Responding to the plea for help, little did she know an old foe was about to emerge...