During the zombie invasion in the Safe House, Tyrone breaks out of his restraints and tries to escape from captivity. However, a zombie attacks Tyrone and takes a bite out of his neck, infecting him. He is saved by Chuck but then is handcuffed to the medical bed, since he is believed to be the perpetrator for the Safe House breach. As a result of his bite wound, he needs Zombrex.
If TK is not given Zombrex and Chuck has completed all cases, it will result in Ending A. When Chuck goes back to get Katey's backpack, he will be attacked by the zombified TK and will get left behind.
If TK is given Zombrex and Chuck has completed all cases, it will result in Ending S, and Chuck will begin Overtime mode where he must defeat him as the final boss and rescue Stacey and Katey.