The zombies have been captured and trapped into a tomb by the humans.
Now they want to escape because they want to revenge their freedom.
Because the place was untouched a lot of time, there are a lot of bats and other obstacles which you have to avoid it, else you will be hurt and you will lose your lives.
If you want to earn more points you have to collect all the bonuses and the powerups which will give you more strength and speed.