 After her last mission (from Metroid 2), Samus Aran finds a Metroid offspring just as she was escaping from Planet SR388. Samus Aran reports the metroid larva to the Ceres space station. But as they were studying it, a fearsome dragon, Ridley, exterminates everything except the larva. This is where Samus finds out about the ressurection of Planet Zebeth.