Megan feels responsible for an agent's death following an explosion at a meth house the FBI had targeted for a bust. When the kingpin eludes capture, it's discovered he may also be involved in child pornography when one of the photographs on his computer turns out to be a young girl in a sexually explicit position. The picture sends Charlie on a crusade of his own, as he remembers a girl he knew as a young child that he suspected was being abused, and he's determined to save the little girl in the picture.

In an effort to find the murderer of an Iraqi woman who had been making a documentary that promoted the rights of Muslim women, Don enlists the help of the victim's cousin. Through her cousin, Don uncovers a connection to Saddam Hussein.

Back at home, Charlie rekindles a romantic relationship with a former girlfriend when she visits him while on a book signing tour.

The problem of the disposal of toxic waste becomes real to Don, Charlie and the team when several children are injured after a sinkhole collapses underneath a school playground. Charlie attempts to help with the case, but faces opposition from his new boss.

Don, Charlie, and the team search for a polygamist who is on the run. The man is on the FBI's Ten Most Wanted List for rape and murder.

When a former mob hit man on death row suddenly has a change of heart and agrees to confess to his crimes, Don has an uneasy feeling about the whole affair.

When a man is found dead, the team enters the world of alternate reality gaming. However, their investigation leads to a danger for a loved one.

A bad case becomes worse when Don and the team must pursue a police officer believed to have committed unspeakable crimes.

When a passenger train collides with a freight train David (Alimi Ballard), Don, and Colby are called in to help rescue survivors and to investigate the cause of the crash

The investigation into a professor's death takes a dangerous turn when the team finds their lead suspect has ties to a radical animal rights group.

A shrewd computer hacker cuts the ground from up under an undercover sting operation to bag a cyber crime lord. His actions trigger a turf war putting his life in peril.

The Numbers team tracks a serial killer who targets johns.