Normal Ending
The final chapter of the game begins with a cut scene that reveals that longtime ally Sullivan is a traitor. You must then fight your way through a horde of zombies to reach the mall's roof. Be sure to pick up some food and a sniper rifle from the "High Noon Shooting Range." Once on the roof you will find yourself in a gun battle with Sullivan. When you win the fight a final cut scene will end the game.
Unlocking Additional Content
Before starting "The Only Lead," the second mission of "Case 7," visit the central grotto of "Fortune Park." Find the two soldiers there and approach to trigger a cut scene. The scene reveals that TK, one of the soldiers, needs a dose of "Zombrex." If you do not give him a dose of the medicine before continuing, no extra content will be unlocked.
Epilogue
The epilogue begins with TK turning on you as well. He kidnaps Katie and gives a list of demands that must be completed before he will let her go. Most of this list amounts to recovering a variety of items from around the mall. When you finish the list you can finally meet TK at the "Fortune City Arena."
Second Ending
The epilogue concludes in a showdown with TK. At the fight's beginning a cut scene reveals that TK has tied Katie to a rope gradually descending toward the zombie-filled floor. You will start the fight without weapons or food, so you should first focus on searching the area to find both. Keep in mind that you can raise Katie by pushing the button on the gearbox in the corner of the room. However, TK will continue attacking while you hold the button, and Katie will begin falling again as soon as you leave. Once you finish the fight with TK a final cut scene wraps up the game's loose ends.