Charlie accurately predicts where a band of bank robbers will strike next. But when Don and his team confront them, a massive shoot-out occurs leaving four people, including an officer, dead. The outcome disturbs Charlie and he retreats into the family garage to work out an unsolvable math problem that he also plunged into after his mother became ill a year earlier. But Don needs his brother's help and tries to get Charlie to return to the case.

When a five-year-old girl is kidnapped from her birthday party, Don and Terry lead the investigation, but must rely on Charlie's help because the girl's father, Ethan, is also a mathematician. Charlie realizes the kidnapper's motive when Ethan reveals he is close to solving Riemann's Hypothesis, a difficult math problem. If solved, the solution could not only earn him $1 million, but could break the code for internet security and unlock the world's biggest financial secret.

A senior computer-science researcher working on a classified government project is found murdered in his Hollywood Hills home and data has been stolen from his computer. The investigation reveals the victim was going through a bitter divorce and was trying to keep his wife from getting his money. Charlie also learns the project on which the man was working might have involved baseball.

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.

An arsonist sets a fire at a car dealership that kills a sales person. The name of an extremist environmental group is spray-painted on the scene, but the group denies involvement. It becomes Don's task to determine whether the group or someone else is responsible. Charlie is called in to help figure out if there is a pattern to the fires that would help provide a profile of the arsonist.

Don and his team investigate an anti-war bombing outside an Army recruiting center that resembles the work of a 1970s anti-war activist who disappeared 30 years earlier after being accused of planting a bomb that killed two people. Retired Agent Thomas Larson, who tried to solve the case 30 years ago, returns to help but questions Don's loyalty when it is revealed Alan knew the radical activist and participated in demonstrations with him, thus causing tension within the family.

An FBI investigation into a computer hacking scam that taps into a bank's system to gain access to the identities and financial assets of its customers becomes personal for Don and the Eppes family.

The case of a dead minor league baseball player leaves Don and the team with more questions than answers. When Charlie discovers that someone has come up with a statistical analysis that can identify which of the players are on steriods, the case gets more leads...and a suspect.

Don, Charlie, and the team take on unknown terrorists who may be using nerve gas to undermine Los Angeles' water supply.