Nash is accidentally shot in the butt by Caitlin, leaving Rick Bettina in charge. Rick is duped by phony FBI agents attempting to swindle half a million in sting money. Cassidy is stalked by a violent classmate.
Harvey discovers his counterculture pal is involved in a murder plot to benefit from a proposed new stadium site. Joe clears his "daughter" accused of stealing jewelry at her department store job. Nash helps Caitlin get into an exclusive VIP party for an artist.
Harvey tracks down two teenage boys who are deadly snipers. Joe has a rat problem in Nash's house, causing a dispute between landlord and tenant. Evan proposes marriage to Cassidy; Cassidy is involved in a deadly auto accident. A case of mistaken identity causes Nash to think Cassidy has been killed.
Nash and company, along with marginal cop Jake Cage, track down pushers of a deadly steroid which makes body builders go hyper-aggressive. Cassidy is haunted by the death of her friend from the auto accident.
Nash and the SIU secretly investigate a plot involving the missing married Governor of California who has fallen in love with a former prostitute. Joe gets stuck with a painting while bidding for someone else at his daughter's pre-school charity auction.
The Bayside Killer resurfaces after a four-year absence, while Nash finally unravels Angel's identity. Harvey's ex-wife Bonnie stops by for a visit. Joe and Caitlin coach rival girl's soccer teams, with Caitlin's new boyfriend as her assistant coach.
Nash and company discover a gang of female bank robbers who plan to break their husbands out of jail. Nick schemes to move into a formerly all-women retirement home. Caitlin readies her negative report on the SIU, much to Nash's consternation.
The SIU is disbanded by MCD: Nash and Joe are assigned to Park Detail, Harvey to Homicide, Evan to Traffic, and Caitlin to Vice. Still, Nash manages to solve a murder involving the Head of MCD's daughter and a drug dealer. Evan and Cassidy announce a wedding date; best man Harvey throws a bachelor party, but finds out the stripper is Anna. Nash tells Caitlin he loves her, but she accepts a job in Boston.
Nash and company, along with Jake Cage, catch three escaped convicts to save the SIU. Harvey has fathered a child with Anna; Evan cheats on Cassidy; Nash and Caitlin finally consummate their relationship.
When a Mexican actress is shot at a premiere, Nash investigates. A reporter who was there, thinks that an actor whom the actress was involved with and broke up with, is the shooter. But Nash tells her to hold off until they have investigated it thoroughly. Later a man claims to have a video of the shooter and will sell it to the highest bidder but Nash arrests him for withholding evidence.
When kidnappers accidentally take the wrong kid, aiming for the child of a rich man, Nash must enlist the help of the man and hope the kidnappers don't find out. Caitlin's housekeeper drives Nsh and Nick crazy.
Cassidy finds an apartment, only to be mistaken for the previous renter who has stolen money from drug dealers. Lonely Joe carries on an online romance, but the other "woman" turns out to be Pepe. Evan bottoms out in his broken relationship with Cassidy.
An embezzler with a twin, along with bumbling Rick Bettina, confound the efforts of Nash and the SIU to recover stolen city funds. Caitlin tosses Nash's baseball out the window after they miss their flight to Jamaica.
Nash investigates a man who may have robbed a bank and is claiming to be have multiple personalities, whoever, Caitlin believes there is more than meets the eye going on. Nick tries to turn his empty life around.
Evan puts himself under suspicion after he takes $40,000 of drug money during a bust; Nash and the SIU take down a drug dealer. Nash and Joe guard a chimpanzee, while Jake Cage goes undercover as an animal extremist.
When a witness chooses not to testify against some punks whom she saw kill someone because her family was being threatened. The prosecutor asks Nash to prove that they threatened the witness and he does. Later the witness is killed. They think the guys tried to make sure she didn't talk so they try to bring them in but one of them is killed. Which now makes them think they have vigilante. And an investigation leads them to suspect the prosecutor and she is belligerent when they question her. In the meantime Evan gets in trouble and calls Cassidy for help.
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.