Jack and Locke put all the guns and medicine in the armory and Locke changes the combo, giving the combo only to Jack.
When Sun is attacked, Jack wants the guns, only Sawyer had told Locke that Jack was coming, so Locke hid the guns. Sawyer shows up with a gun, saying there is a new sheriff in town. With the help of Charlie, Sawyer had conned Jack, Locke, and Kate in order to play Jack and Locke against each other and gain control of the guns. Charlie helped because he wanted to make Locke look and feel like a fool.
In flashbacks, Sawyer pulls the same old con on a woman named Cassidy, but she figures out it's a con and asks him to teach her how to con. The two are together for awhile and they con people together, but what she doesn't know is that he has been conning her from the beginning.