Defender is an updated version of the classic arcade game. The Manti bugs have invaded Earth, and human survivors now live in colonies throughout the solar system. As more swarms of Manti arrive, even the colonies are threatened with being wiped out. You've been enlisted to help save the remaining colonists and destroy the Manti bugs! There are six different ships to fly, each with its own flight characteristics and special weapons. Power-ups can also be found throughout the missions.
Gameplay involves navigating through increasingly difficult levels while avoiding Manti and destroying them. Captured humans can be rescued before they're converted into mutants, which will increase the attack force of the swarms. You'll earn credits by saving colonists, which can be used to purchase improved weapons or shields for your ship.