The parents of a seemingly perfect family are murdered; Curtis grapples with his new position; Megan's romantic life heats up.

When two young girls are in a tragic car accident, one is left in critical condition and the other is found dead at the scene. As Megan and her team investigate the case, however, they realize there has been an awful mistake. Not only was the wrong girl pronounced dead, but the car accident may not have been the actual cause of death.

When a city-wide outbreak of a mysterious and lethal virus occurs, even Megan and her team are at risk. In order to determine who and what caused this outbreak, CDC Officer Charlie Stafford takes over the investigation.

The team needs to quickly figure out how to treat the virus when more and more people are becoming ill and dying.

Megan comes face-to-face with a convicted serial killer she helped put away.