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.

Kate becomes involved with a man she met at a political event, but when a young Russian girl is found dead, she suspects that he may have something to do with the murder, and looks to Megan for help.

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

A schizophrenic teenage girl at a mental institution is found murdered. When Megan and Tommy interview a young patient named Darby, who seems extremely sane and lucid, she tells them that she saw the killer climb down from a heating vent in the ceiling, but most shocking of all -- he meant to kill her, not the actual victim. Could the killer be Dr. Malcolm, the ward director, who is obstructing their investigation.

Megan's father's exhumation uncovers more questions about what she always believed was a suicide, and her mother suggests she examine his patient files for clues about his death and that of a patient.

Megan suspects foul play when a young philanthropic socialite dies; the investigation is interrupted by Kate's personal life.

When a young nanny is run down by a car and killed, the 5-year-old child she was watching is kidnapped; an interrogation goes awry.

When a recent lottery winner is found brutally murdered, everyone becomes a suspect.

When a severed hand and foot turn up in a back alley, Megan and her team must literally piece the victim back together. Meanwhile, Megan's daughter, Lacey, gets her mother's reluctant permission to visit her at the office and film her at work as part of a video essay for Social Studies class. What Lacey learns in the process profoundly changes her view of her mother

Curtis questions Ethan's interest in the investigation of the mysterious death of a beautiful twin; Megan runs into resistance while investigating the death of a patient at the hospital where she used to work.

Many suspects emerge after a rich tycoon's new, young wife is shot during a deer hunt; Kate and Megan's relationship takes a turn for the worse.

A murdered young woman's body turns up in place of a medical school cadaver during class, leaving Megan to rely on the aid of the star student to help solve the case.

When the owner of a family owned and operated Italian restaurant turns up dead in the freezer, Dr. Hunt and the team take a closer look into family matters. Meanwhile, Peter must face his own haunted past.

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.

A murder victim's rabid neighbor bites Tommy, and after another rabies fatality, Megan calls on the new health commissioner to aid in their investigation.

When a young girl is found murdered, Megan has to put her personal doubt aside and help a blacked out Tommy, covered in blood, prove his innocence.

Gerry Roberts, in trial for defrauding his investors of a billion dollars, is kidnapped in front of the court house. The getaway car runs over a protestor and later, the team has to decide whether a video of Roberts being killed could have been faked by himself. Meanwhile, Megan gets closer to the truth about her father's death.

An inmate violently escapes from a prison transport van and becomes a dangerous fugitive on the run in Philadelphia. Soon another man turns up dead - who's revealed to be a witness in the escaped prisoner's murder trial. Megan must continue to search for the truth in the original case when the accused murderer shows up and pleads with her that he is innocent and being framed.

Megan is surprised to discover she has a connection to a woman found dead in a hotel room; Megan starts taking an interest in what is going on around her.

The investigation into a fatal car crash reveals the seedy underbelly of a perfect-looking neighborhood.

After Peter rescues a woman from a house fire, Megan discovers another person in the house who died. Peter takes the discovery personally since he had no idea anyone else was in the house. A veteran arson investigator challenges Megan at each step in her investigation. When Megan complains to Kate the response she gets only intensifies the tension between the two women.

A champion equestrian is killed and potential drug use is suspected, but when Megan's daughter, who also rides, overhears details of the case, she leads the team to a clue and possibly the murderer.

A pharmaceutical rep is found dead in the Schuykill River, but when Megan Hunt and the team investigate, there's no blood found in her body. The team must locate the original crime scene to see if they can find the cause of death, but with suspects who have access to hundreds of unknown drugs, they may never know who or what killed her.