"Metroid Prime 2: Echoes, known in Japan as Metroid Prime 2: Dark Echoes (メトロイドプライム2 ダークエコーズ), is a first-person, action-adventure video game developed by Retro Studios and published by Nintendo for the GameCube video game console. It is the seventh game in the Metroid series, a direct sequel to Metroid Prime, and the first game in the series with a multiplayer feature. Echoes was released in North America, Europe, and Australia in 2004, and in Japan in 2005.
The events of Echoes are set 6 months after Metroid Prime. The story follows bounty hunter Samus Aran after she is sent to rescue Galactic Federation Marines from a ship near Aether, a planet inhabited by a race known as the Luminoth. There, she discovers that the troops were slaughtered by the Ing, an evil race that came from an alternate dimension of Aether. Samus must travel to three temples to ensure the destruction of the Ing, while battling Space Pirates and her mysterious doppelgänger called Dark Samus."
Source: Wikipedia, "Metroid_Prime_2," available under the CC-BY-SA License.