In the bunker they have to put in the code that got the fat kid there every 108 minutes. If not it is thought that the world will end. The guy that was in the hatch was doing it by himself for a long ass time so he convinced Lock that if the code isn't entered the world will end, thus replacing him so he can go scott free. Jack wasn't buying it, but eventually caved so now they're trapped into running shifts putting in the code because they're scared. I haven't watched tonight's episode yet, I got it on digital record.