You stayed at a safe bunker because of the apocalypse. It has gone worse. One day you hear a knock on the bunker which sounded like desperate knocks. You check the cameras and see Gray knocking on the door desperately. You change to another view of the camera and see two infecteds behind Gray. Luckily they were 20 meters away bit they were getting closer

Gray's voice is faintly head through the cameras

"PLEASE LET ME IN PLEASE LET ME IN"