Space cows have invaded the earth with the intent to devour all the plant life.
Humans have been captured to become space farmers, so that cows don't need to invade other planets anymore as the process of finding a new planet takes too long.
You play the game as Moo Cownor, the only member left alive from the resistance.
Your mission is to keep the remaining invader force at bay while also building a spaceship powerful enough to space jump into the Cowfederation's galaxy, to rescue the humans (why though?) and eliminate the threat.