Another of Dr. Wily's schemes has been defeated and peace has returned to Earth. Or so it seems. During a peaceful walk with his sister Roll, Mega Man is confronted by a powerful alien robot called Terra who falls from the sky and defeats him instantly — then dispatches an army to conquer the planet. Mega Man wakes in Dr. Light's lab with a new weapon: the Mega Arm. Now he must blast through waves of robotic enemies, use weapon upgrades, and solve the mystery behind an alien invasion nobody saw coming.