You have just been hired by Core Juice. This is basically the Coca-Cola of the alien race. You job is to invade various different planet and drill into the core and extra the juice from the planet. You know kind like we humans do with drilling for oil on Earth. You main objective is to protect the drill and it's work by defending against the alien natives. To do this you must research new upgrades to put new units into battle and make your current units string and upgrade-able. This is a new job and you have a lot to prove to the big wigs upstairs so you must not fail!