The team investigates the theft of a graphic comic book.

The team investigates a crew stealing high-end goods from a shipping service; Don questions his faith in the FBI when one of his men is killed on duty.

The FBI becomes involved in the stalking of a popular singer after she is threatened by an intruder in her house and reveals a series of threatening letters she's received through the mail. Charlie determines the letters are from two different people after analyzing the handwriting. When a photographer is found dead near the singer's house, Don believes the photographer was murdered and his death is somehow related to the stalking case.

A feud between Chinese gangs leads to the kidnapping of an undercover agent and the reappearance of Samuel Kraft.

Don and his team are out to protect former radical Benjamin Polk from a determined sniper who wants him dead, and who is leading the FBI on a cat-and-mouse chase as he closes in on his prey.

The FBI becomes involved when the bodies of young Asian girls are washed up on the beach. The situation becomes more critical when it is discovered one girl has avian flu. As the investigation continues, Don and his team discover a connection between the girls and the sex trade industry. Meanwhile, Amita considers a transfer to Harvard University, which causes Charlie to re-evaluate his feelings for her.

When a researcher who specializes in Native American antiquities is killed at the museum where she works, the FBI is called in because the museum is on federal land.

A murder investigation at a Los Angeles card club leads the FBI to a complicated card-counting scheme involving college students.

When Don and his team are called to the scene of the murder of a Los Angeles gang member, they learn they are investigating the murder of another agent who had been working undercover.

Don and his agents are asked to investigate when a search team finds three dead women in the wilderness who were apparently murdered under bizarre circumstances. The case becomes more suspicious when Don learns the search team was led to the crime scene by a psychic. When the psychic offers to help the FBI in solving the crime, Charlie is determined to prove the psychic is a fraud.

Don and the rest of the team investigate several attacks occurring on LA highways that may be connected.

Don and his team must race to save the hostages being held on a hijacked bus.

To help capture a serial rapist-turned-killer, FBI Special Agent Don Eppes recruits his genius brother Charlie, who uses a mathematical equation to identify the killer's point of origin by working back from the crime scene locations.

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.

Don and Agent Weston of the NTSB investigate eyewitness accounts of a mysterious unidentified object flying dangerously close to downtown Los Angeles that has raised concern of a terrorist attack. After Charlie is recruited to help with the investigation, it is discovered that the flying object is part of a new technology that could revolutionize air travel. But the investigation takes a turn when they learn that the lead engineer is found murdered.

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.

A man wanted for stock fraud is found garroted in his apartment, and the crime is eerily similar to a murder committed a year earlier, a case in which Don closed when an ex-con confessed. Now, Don must re-investigate the old case to determine if he put an innocent man in jail. He asks Charlie to go over the evidence to see if he missed anything the first time around.

A dangerous felon escapes when a prison bus crashes and the FBI has reason to fear he's intent on revenge against the witness whose testimony put him in jail. However, finding the elusive killer proves to be a complicated challenge. Don teams up with Agent Billy Cooper, his former partner from the FBI's Fugitive Recovery Division, and Alan worries that Don's going to return to a more dark and obsessive time in his career.

Don and Charlie investigate the murder of a judge's wife who was shot in her garage. It's unclear whether she was the intended target or her husband, who was hearing a death penalty case involving a gang leader. As the investigation continues, Don reconnects with a prosecutor whose life may also be in danger.

Don uncovers a secret code that begins the hunt for a skilled and trained assassin, and the efforts by the FBI to save the life of a Colombian exile living in Los Angeles.

When a father is killed in a home invasion, Don and his team investigate the connection between the murder and a rash of robberies in the upscale community.

When a car crashes into a busy coffee shop, the team discovers the fatal act might not have been an accident.

Don investigates the murders of two young women found in their cars outside their homes. Their deaths were made to look like drug overdoses, but Don realizes a serial killer is responsible. Meanwhile, Charlie is having bizarre dreams about his parents. In one dream, his deceased mother appears and tells him he has a question to ask her, but he can't imagine what it could be.

Various people in the L.A. area with seemingly nothing in common start to become extremely sick and die on the same day. Don fears bioterrorists may have released a deadly virus into the environment. While he tries to discover whether anyone is behind the outbreak, Charlie tries to locate the point of origin.