Aliens have planted human cloning machines in the DOWNTOWN areas that corrupt the human DNA and turn them into zombies. We have to disable the machines but the task is not easy, first the area where the machines have been planted should be cleared from zombies. Once the area has been cleared the Alien Boss arrives. In order to gain the Access key, you have to kill the BOSS. Once the BOSS is killed you will get the Access key which you can use to disable the machine.