Your ruined science outpost is under attack by horrible creatures, and you have to last a year before anyone comes to check on you.
When the zombies attack, you'll start running automatically. It's up to you to chosen when you fire, sprint, hack with your axe, and general fight back to prevent them from your reaching your base before you do. Or, if you're feeling really tough, you can try to destroy them all before they reach your base.
Choose your upgrades wisely?
This game is played totally with the mouse.