You're a pixelly dude fighting pixelly zombies on the streets of London. There's a butcher shop, a dog pound and a gun store for your convenience. All three have helpful items to help you fight zombies, but it's going to cost you.
The currency in this game is number of zombie kills. Spend it wisely because the more you kill, the higher the level, and then you unlock bigger and badder zombies to fight. The nice thing about the level system is that when you die, you can retry the current level you were on, but you get to keep any kills you had from your previous attempts.
There are cars and buses scattered around the streets too, which you can use to shield yourself from zombies. Though they are fairly strong, they won't last forever, and can be destroyed by zombies or by shooting them. When they explode, they can release a health pack, a temporary speed powerup, or a chainsaw which makes you invincible while you have it.