The planet Latis is under attack by the Space Dragon Salamander, its war planet, and the Bacterian horde, which is destroying everything in sight; Latis's defenses are ineffective, and its people are losing all hope. Three heroes from the planet Gradius join Lord British in defense of his beloved planet Latis. Then, in a prequel, a girl from a distant planet brings an ominous warning to the planet Gradius, concerning the Bacterium, which the three heroes must investigate. The third episode jumps to the future: after the signing of a peace treaty, one of our heroes is captured by the Bacterians. The military of Gradius and the remaining heroes must save the prisoner from a fate worse than death.