Not long after her victory over the Space Pirates on the planet Zebes, bounty hunter Samus Aran intercepts a distress signal from the derelict Space Pirate frigate Orpheon, whose crew has been slaughtered by their own genetically engineered experiments. After battling through the ship and narrowly escaping its destruction, she pursues a cybernetic incarnation of her old foe Ridley down to the nearby planet Tallon IV. There, Samus discovers the ruins of the Chozo, an ancient race wiped out decades earlier when a meteor struck the world and spread a corrupting, mutagenic substance called Phazon. As the Space Pirates work to harvest this dangerous resource for themselves, Samus explores Tallon IV's varied and hostile regions, piecing together the fate of the Chozo and the growing threat the Phazon poses.