The player takes on the role of the commander, tasked with defending bases, colonies, space stations, and outposts from waves of aliens attempting to grab and escape with the power cores housed in each location. The player views the game from a top-down perspective and has the ability to build various towers that attack and route the path for the waves of aliens. Once an alien reaches the power core housing, it will make its way back towards the exit. If the alien is killed on its way back, the core will drop and slowly float back to the core housing. Different towers provide various abilities that are good against different types of aliens so the player must build a strategy to defend the cores against all waves of aliens.