While coming home from a late night bachelor party, Nash and some of his fellow cops become embroiled in a train heist gone bad on a BART train.

After a nearly 20-year absence, the notorious San Francisco serial killer, ""Zodiac,"" returns to taunt Nash as well as haunt Nash's mentor (who has since retired). But is it the actual Zodiac, or just a lethal copycat? Meanwhile, Joe goes undercover as a bike messenger to nab a free-wheeling drug dealer.

Nash is stuck with an eleven year old delinquent who's the link to busting a drug kingpin. Joe is reunited with his grown son J.J. and Nick wreaks havoc with Nash's attempt to find him a live-in nurse.

Nash and Joe cut a deal with Carlos Casas, a gangland money launderer, offering him a new identity in exchange for his testimony.

It's Christmas Eve, and Nash and his fellow cops are trapped at the SIU as they wrap up a murder investigation and a prostitution case. Joe borrows Nash's 'Cuda to get it detailed and freaks out when the car is stolen; Nash's personal gifts to Lisa and Whitney get mixed-up; personal crises abound as the cops deal with the Christmas holiday.

Nash and Joe have a task of escorting a secret key witness from the Witness Protection Program to San Francisco to testify in an important SIU-related case. They fall under gunfire. Nash realizes there's a leak somewhere on the prosecution's team. He enlists the help of Stacy to protect them until he can solve who it is and get the witness safely to San Francisco. Cassidy is stood up for a date and decides to go out with J.J. instead.

Joe goes undercover inside State Prison to bring down a ruthless Mexican gang leader who put out a hit (from behind bars) on a SFPD undercover cop who had infiltrated the Mexican Mafia. Nash runs the investigation on the outside, hoping to fulfill a promise to the dead man's widow by catching the trigger man. Naturally he'll have to overcome the distraction caused by Nick, putting together his will, who discovers some long-forgotten wealth.

Nash busts computer hacker/robber, Andy, and discovers Andy's committed the crime because his wife has been kidnapped. The crew of crooks want Andy's hacker skills as their ransom. The SIU must work to save the woman and bring down the crew before their daring daytime robbery is successful. Meanwhile, Nash and Whitney finally consummate their relationship.

After Cassidy is hit in the behind by a stray bullet at school, Nash and Joe go on the hunt for the shooter and the dealer who's putting guns into kid's hands. Due to earthquake repairs on his apartment, Nash and Nick have to take up residence with Lisa for a few days. It's here that Nash meets Freddie, the apple of Cassidy's eye, the pain in Nash's behind, and learns that Cassidy's decided not to go to college.

Hot on the trail of a murderous criminal from Chicago, Nash teams up with a KAREN DECKER, a cop from the Windy City who's in every way his equal: smart, competent-and yes, sexy. Sparks fly between them as they track down the visiting villain together -until, that is, Nash learns his newfound partner is not as perfect as she's led him to believe. Joe, meanwhile, hires a pet psychologist to cure what ails Nick's racehorse, Mr. Woody.

Nash's old nemesis from the SIU, Rick Bettina, now a bounty hunter, is back and in competition with Nash as they both try to track down mobster Ray Goetz, who Bettina wants on assault and battery charges in Vegas, and Nash suspects of ""hitting"" a high-level mob boss. Meanwhile, Joe fears repercussions from Inger after losing his wedding ring.

Nash solves murders in Chinatown and helps out an old friend, Cedrick Hawks, a professional gambler who is in San Francisco to clear up a bad debt.

Nash and Joe butt heads with the leader of a team of Urban Commandos who has been hired to protect an inner-city community. While awaiting the birth of the new baby, Joe searches for the family crib that he lent to Nash seventeen years ago.

A busload of San Quentin prisoners on their way to court is hi-jacked in downtown San Francisco. Nash has to track down two dangerous escapees, including a paramilitary activist who seeks bitter revenge on Nash.

Nash's sister, Stacy, is robbed, forcing her to come out of the closet as a lesbian. Nash deals with his own secret romance with Nick's nurse Whitney. The fallout from these family revelations takes place while Nash tracks down a kinky couple responsible for the robberies.

Nash follows the trail of James and Lorraine, a thrill-seeking couple on a wild crime spree in San Francisco. Nash feels personally responsible for the fate of Lorraine when he discovers she is the daughter of a volatile SFPD Inspector. Nash's interaction with the young fugitive color his relations with Cassidy, who's semi-nude photo is splashed all over town in a racy safer sex poster.

A small time getaway driver sets up two robbery gangs to rob each other, while he walks away with the loot and complete immunity. Evan is brought in for another chance in Joe's off-duty case concerning a kidnapped son who has had a gender change. The 'Cuda hood is graffitied, and Nash puts Boz Bishop on the case.

Nash, while investigating an apparent gang killing, discovers that the weapon used for the job is the Army's newly missing man-portable, antitank system: The Javelin. Nash is assisted in the investigation by Sandra McCormick whoose career is on the line if the Javelin is not recovered.

Nash investigates a judge's murder, and unwittingly triggers an Internal Affairs investigation. The Internal Affairs cops go bad, and only Nash Bridges and the SIU can stop them.

A first-rate professional robber and his crew hit San Fran in a string of strong-arm jobs. Joe convinces Nash to moonlight as a private eye, searching for the SF Giant's short stop's missing car.

A world renowned hit-man has been hired to kill the chief witness in a far reaching drug prosecution. Nash Bridges must stop him. Only problem is, the hit-man turns out to be one of Nash's closest boyhood friends gone bad. Meanwhile, Evan works a stakeout with Bryn and gets sidetracked when he falls in love with a woman living upstairs from their surveillance target.

A people-smuggling ring brings Nash and Joe to the aid of a young man searching for his parents.

Nash and the SIU uncover a counterfeitering group where the money is top-of-the-line Supernote quality. Moving in to bust the group, they discover a fake SIU gang impersonating the police. Cooperation becomes tense as suspicions abound over who and what to trust. In the interim, as Nick gets in over his head financially with his horse costs, Nash reluctantly agrees to work with Joe on an off-duty case searching for a Super Bowl ring. However, Nash and Joe soon find themselves impersonating a gay couple as the case develops differently than Nash anticipated.

Nash and Joe have to babysit Mickey Tripp (Paul Gleason), a motormouth shockjock, after a body armor-wearing assassin tries to kill him. Their search for the assassin is compounded by the fact that Nick has hired them on an off-duty case to find his softball team's star pitcher - a Salvadoran defector named Chus (Jose Canseco), who's on the run from the INS (Karl Malone). Caitlin babysits her roommate's kids.

Nash and Joe risk causing an international incident after British consulate workers fake the death of a convicted killer in order to use him for their own nefarious purposes. Joe resorts to extreme measures in order to get Lucia accepted into an ultra-elite school.