Plot

Earth is under attack by a monstrous race of gigantic living ships known as the Reapers. Even if Commander Shepard could unite all surviving species in the galaxy, only a miracle could save them. Then again, Shepard did come back from the dead.

Retake the galaxy as the legendary Commander Shepard; save the galaxy from The Illusive Man and The Reapers alongside the rest of the Normandy's crew. The fight for humanity is here; and the Mass Effect Saga draws its conclusion for The Shepard Trilogy.—Johnny-the-Film-Sentinel-2187

Mass Effect 3 begins on Earth with Commander Shepard having been detained following the events in Arrival.Out of the blue, the Reapers attack and the planet is overwhelmed. Shepard escapes a burning Vancouver on the Normandy with the help of Admiral Anderson and leaves to gather help from other species while Anderson coordinates human resistance on Earth. Before leaving the Sol System, Shepard is ordered to Mars by Admiral Hackett who claims that researchers have uncovered something that may give humanity a chance against the Reapers. There, Shepard battles Cerberus forces and encounters former squad-mate Liara T'Soni, who has discovered plans for a Prothean superweapon that may be capable of defeating the Reapers. Before leaving the facility, Shepard speaks with the Illusive Man, who claims he wants to use the Prothean weapon to take control of the Reapers