The earth has become inhospitable, so humans have created an Ark to travel through space and find a new home. You have been sent with a small contingent to scout ahead and find a suitable planet. Unfortunately, an alien invasion begins before the Ark gets there -- hold out from 30 waves and protect your new home!
Tutorial at the start of a new game; press ESC in game to see all controls and review the basics. Mouse controls character movement. Click an outpost to get inside, left click to shoot, space bar ejects.