After many frustrating years, scientists have finally made contact with biengs from another planet. That's the good news. The bad news is that these aliens are bent on conquering the galaxy one planet at a time. After discorering the existence of the Earth, the aliens send troops to our world in the hope of enslaving it. These soldiers are determined to reach the surface of our planet, and if they succeed, the human race is doomed. Fortunately, the people of Earth are prepared for this assault, building protective barriers over key military outposts and manufacturing powerful mobile cannons known as "bases". The bases are our best defense against the invaders, -but beware... The enemy won't quit until they've won, and they'll destroy everything that stands in their way... - And that's also including you !. The Rainbow effect... If the final aliens you kill are in the bottom 2 rows, you get a fireworks display and 500 bonus points. If it happens to be the bottom, left-most alien, you get fireworks and a 1,000 point bonus.