Megan knows the CDC must be working on a cure for this thing. She gets Charlie to admit that there's an experimental drug that's in the works. Megan wants him to use it on Kate, who is grateful to see a friendly face when Curtis visits her. As for the experimental drug, Charlie breaks the law by using it on a patient. It's not Kate. It's the guy Dani met at the bar. He's their best bet since he's remained alive the longest… until now. The guy has a fatal reaction to the vaccine. It seems there really is no cure. That means Kate is almost out of time.
Bud, Sam and Peter realize the terrorist typically spreads the disease one location at a time. Peter realizes that one of those locations was a mobile one—like a bus. Security footage shows all of the victims from the list of outliers boarding the same bus. They all touched the railing that had been infected by the killer a few hours earlier. They identify him a disgruntled former worker at a lab that stores bio-hazardous strains.
Megan realizes that two of the outliers had bedbug bites that may have come from the same hotel where the killer stayed. They raid the place. The terrorist is gone, but likely not far. Sam, Bud and Peter realize he's headed to a subway entrance to infect the railings. They corner him on the stairway. When the man charges, Peter shoots him dead in the head.
The terrorist is gone, but the terror he spread lives on in his still-dying victims. Megan realizes that the first recipient of the experimental vaccine died because there was alcohol in his system when he received it. That means the drug could still work. Kate is living proof that it does. She wakes up surrounded by all of her colleagues, surrounded by all of her friends.