Lost Contact is a base defense game where you are trying to defend your power source and find a control sphere to connect to by growing your base.
You have to use different types of towers for your advantage and keep the power source and the towers you build connected at all times or they will not function at all. That's how they are powered.
Who are you defending the power source from? A primitive alien race that invaded Earth, now it's time to wipe off the human race off of galaxy.