Officers Jim Street and Robert Duran of the WCPD's Olympic Precinct, dispatched to a fake emergency call, are ambushed by a trio of cop killers; the newly-established Olympic SWAT team arrives, led by Lt. Dan "Hondo" Harrelson, but the gunmen escape, leaving Duran dead and Street devastated. The shooting is just one more casualty in a series of ambushes by the trio to avenge the death of gunman Dallas's uncle, allegedly in police custody. Street opts to attend SWAT training in the hopes of avenging Duran, and Hondo selects Street for the team alongside natural marksman Travis Joseph "T.J." McCabe. The attacks continue as the gang prepares one final ambush before fleeing the city, but SWAT catches on and moves to disrupt them; in the ensuing operation, two of the gunmen are apprehended and Street kills the last, but he realizes revenge is meaningless and can never satisfy him. As the gunmen are booked, Hondo reveals their revenge was based on a misunderstanding—Dallas's uncle had killed himself to avoid arrest—and muses on the pointlessness of killing before returning to duty with his team.

Joey Hopper is broken out of a hospital prison ward by the Hopper family, a violent Satanic cult led by Joey composed of disaffected youths, responsible for a string of brutal murders and narcotics crimes. As Olympic SWAT joins the citywide manhunt for the Hopper family, Hondo finds himself targeted by Joey for having apprehended him earlier, while an underground newspaper editor at odds with the WCPD turns to Hondo for help when his daughter is drawn into the Hopper family. Tracking them down to a remote farmhouse, SWAT besieges the Hopper family and uses tear gas to smoke them out, while Joey is killed when he takes the editor's daughter as a human shield. With the threat subsided, Hondo celebrates his anniversary with his wife Betty, initially interrupted by the manhunt.

Frank Thomas is shot and killed by a sniper on the freeway, the third in a string of calculated yet seemingly random sniper attacks. As Olympic SWAT investigates, they learn two of the men dated the same woman, fashion model Janet Warren. Hondo devises a plan to draw out the sniper: having a SWAT officer go undercover as her new boyfriend. Street is selected for the role, and gradually falls in love with Janet, but becomes targeted by the sniper, Eric, a dressmaker working in Janet's company seeking to make her fall in love with him. When Eric kidnaps Janet, Street catches on and trails him to the coast, where SWAT battles him while Hondo scales a cliff to flank him, eventually reaching Eric and Janet in time to kill Eric before he can kill Janet in a murder–suicide. Though she is no longer under threat, Janet, shaken by the losses she endured, decides to leave the city, and visits Street and the team one last time to bid farewell.

With Olympic SWAT considerably busy handling standoffs and monitoring an APB on a kidnapped high school girl, freelance writer Meredith Cooper is embedded with SWAT for a human interest article in a magazine. Cooper is infamous in the WCPD as a staunch police critic who views SWAT as "a necessary evil, but more evil than necessary", but they cooperate nonetheless. However, the day's difficulties worsen when Hondo, already struggling with SWAT calls interrupting his family life, is called to the hospital during a standoff after his son is struck by a car. Later, SWAT is deployed for a plainclothes takedown when the kidnapped girl is spotted on a ferry, but when Cooper follows the team aboard and unintentionally provokes the kidnapper, the officers are forced to shoot. With the day finally over, Hondo finds time to get his family life together.

Infamous drug kingpin Vincent Ritchie agrees to testify against his former associates before a committee, but is critically injured and hospitalized after his police escort is ambushed. Olympic SWAT is assigned to the hospital to protect him, while Dominic Luca enters a relationship with his disaffected daughter—but the situation becomes tense when a police ploy uncovers a mole in the hospital staff, sent to confirm Ritchie's death. With Ritchie scheduled for one final surgery, his former associates deploy a team of hitmen to assassinate him by any means necessary, but SWAT manages to fight them off, only for Luca and Hondo to catch Ritchie's daughter trying to kill him on her own terms. Ritchie ultimately survives and reveals dozens of crime bosses to police and the public, while Luca accepts he is still single.

Bo Pritchard, Hondo's comrade from the Vietnam War and a known cowboy cop trying out for SWAT, joins Hondo and David "Deacon" Kay at the scene of a botched burglary. When Deacon is shot by the suspect and Bo shoots the suspect despite the team having him at gunpoint, Hondo chooses to hire Bo as a temporary replacement while Deacon is hospitalized. However, Bo's violent and uncooperative nature leads to tensions between him and the team, worsened when Bo covertly threatens Deacon with full replacement in SWAT. When Bo escalates another hostage-taking and forces T.J. to shoot the mentally-disturbed suspect, Hondo kicks Bo off the team. Bo suffers a mental breakdown and kidnaps Betty to draw Hondo out to fight him personally; Hondo obliges and, after a brief fistfight in a warehouse, manages to defeat Bo and rescue Betty. In the aftermath, Deacon fully recovers and is brought back to the team.

Olympic SWAT responds to a sniper targeting an ambassador, committed by the "Organization for the Freedom of Oppressed People", purportedly a Middle Eastern left-wing terrorist group active in California. Unbeknownst to the police, the Organization is actually a front for a criminal group, part of a complex plot to rob the Owls basketball team (one player of which, Ollie, is a longtime friend of T.J.'s) for $2 million, using the terrorist charade as a way to pressure the authorities into acquiescing to their demands. When the group launches their attack at the Sports Arena and takes the Owls hostage, Hondo's attempts to negotiate a release are stymied by political pressure and the wounding of a player, and he is forced to follow their demands. However, quick thinking from Ollie and strategic placement of the team leads to the entire group being apprehended and the Owls being freed.

Olympic SWAT is assigned to protect a U.S. Senator, known for his strong anti-gambling stance, and rescues him from an attack by frogmen. With the attempted assassination a failure, a gambling magnate hires a professional hitman from overseas, who steals an ArmaLite AR-18 from a National Guard armory and prepares an ambush while enjoying himself in the United States. However, when several people the hitman comes into contact with—including the gambling magnate, a National Guardsman, a young boy, a waiter, and his date—fall ill with a severe form of pneumonic plague last reported in India, SWAT is pressured to find the increasingly-ill hitman before he potentially sparks a deadly epidemic. The hitman's attempt on the Senator's life fails, and SWAT pursues him to a water reservoir, but he falls in and dies before he can be apprehended.

An empty armored car is stolen from a security company overnight. Though no valuables were stolen, Olympic SWAT is alerted, as the armored car is practically impenetrable and could be used for anything from robberies to terrorist attacks. As SWAT follows up on the armored car theft, T.J. brings Luca to the American Beauty Contest, where his fiancée Susan works as a photographer; unbeknownst to them, the contest is the target of the armored car's thieves, a gang of veterans seeking to steal the bejeweled crown and scepter worn by the winning girl, worth over $2 million. The gang disguises themselves as the armored car crew scheduled to retrieve the crown and scepter, but takes Susan and the winning girl, Miss New Mexico, hostage in the armored car when they learn the crown and scepter used in the event is a fake copy, stealing the real one from the event organizers. SWAT surrounds the van and, after an intense standoff, manages to use paint shells and a flare launcher modified to fire gas to smoke out the fake guards and rescue Susan and Miss New Mexico.

At Street's university, students prepare to protest the Biological Weapons Convention, which they believe was not followed by the U.S. military, and an alleged experimental biological warfare program by Omega Chemicals involving Dr. Brunner, Street's professor. However, a group of radicals led by Stockwell use the protest as a cover to take over the Omega One chemical plant and demand a $1 million ransom lest the plant explodes, taking Brunner and his wife hostage. Olympic SWAT, following up on a gun shop robbery related to the radical plot, is alerted to the attack. With the radicals setting a deadline of just three hours, Hondo delivers the ransom while the rest of the team infiltrates the plant to apprehend the gunmen. After Stockwell takes Hondo as a human shield and T.J. shoots him, Brunner remembers the plant's override code—the date of the attack on Pearl Harbor, Franklin D. Roosevelt's "day of infamy"—preventing the explosion and saving the city.

During a standoff at a massage parlor, Hondo is grazed in his head. Though he survives and refuses medical attention, the injury begins to take its toll: his vision blurs, he becomes disoriented and aggravated more often, and he nearly faints at a standoff. Finally accepting the injury affected him more than he thought, Hondo learns he has a concussion and decides to retire from frontline duty, handing command of Olympic SWAT to Lt. Purcell, a rough commander from Riverside Precinct who is often at odds with the team. However, Hondo decides he is dissatisfied with desk work and opts to undergo a risky surgery to undo the damage. The operation is a success and Hondo returns to commanding Olympic SWAT, successfully resolving a hostage situation through negotiation alone.

Olympic SWAT shoots and arrests a gunman in an amusement park, devastating his young son, who may be without parents as his mother is hospitalized following a heart attack. Simultaneously, a former parole officer scopes out SWAT's response in preparation for a heist at a coin collection auction; his crew plans to use a series of random shootings and explosions as a diversion. When the boy runs away from his youth shelter, Hondo eventually finds him checking on his mother, and offers to let him stay in the Harrelson household for the time being. Later, the heist is pulled off, and the diversion is launched; the police are initially fooled, but SWAT catches on when a silent alarm at the auction breaks from the pattern. The team deploys to the auction and apprehends the heist crew. The boy's mother eventually recovers and takes custody of him.

The S.W.A.T. team is asked to help apprehend jewel thieves who are committing robberies, taking a female hostage each time, and making their escape underwater using SCUBA gear.

Following a training exercise with S.W.A.T. officers from another division, Lt. Harrelson and Street find the dead body of Officer Frank Baylor (played by Don Eitner) with the words "Kill S.W.A.T." pinned to his chest. The murder of Baylor is the forerunner of a series of attempts to wipe out S.W.A.T. by two brothers and their fanatic sister-in-law, who is convinced that the death of her husband was the result of S.W.A.T. brutality.

When local police are overwhelmed by a series of crimes committed using automatic weapons, S.W.A.T. is called in, sending officers Dom Luca (Mark Shera) and T.J McCabe (James Coleman) on an undercover assignment to discover the source of the weapons.

The team is trying out one of their new devices (a beeper) at a movie studio. When they have finished, Officer Street (Robert Urich) mistakenly leaves his behind. He picks up his girlfriend and goes back to get it, but in the interim, someone planted explosives all over the studio as part of an extortion scheme.

Mel Lang (Paul Mantee) and Ralph Costa (Aldo Ray) have just been released from prison after serving five-year sentences. They were reported to police by construction magnate Carl Rigby and arrested by Sgt. Harrelson. When S.W.A.T. is called upon to assist police in evicting heavily armed brothers Will and Johnny Brewer from a home being taken over by Rigby, Lang and Costa see their opportunity to execute Rigby and Harrelson, and to create evidence pointing to the Brewer brothers.

Two transient teenagers seek shelter in the warehouse of Colby Electronics. While they are there, three men break in and the female teen anonymously calls police. Before fleeing, the boy gets a good look at the robbers, one of whom is Greg Colby (played by Carl Betz), a prominent citizen and former U.S. Senator. Subsequently, Colby befriends Lt. Harrelson in an attempt to discover the identity of the teens, with the intent of killing them.

Paul Julian (played by Harris Yulin), a radio repairman and ham operator, has patched in on the S.W.A.T. radio band, where he listens in on calls. This allows him to arrive at crime scenes ahead of S.W.A.T. and find concealed observation positions. Bent on avenging his wife's murder, he kills two disarmed gunmen who have been talked into surrendering by Lt. Harrelson, and leaves S.W.A.T. facing intense media pressure and accusations that they are behind the senseless killings.

When S.W.A.T. moves in to combat a race track heist involving a female hostage, Howard Wilson (played by Bill Fletcher) is captured while his accomplices Mike Simon (Robert Webber) and Frank Peterson (Zitto Kazann) escape. Wilson is on the brink of revealing the names of his accomplices when high-powered attorney Jason Bridges (H. M. Wynant) assures him that Simon and Peterson are planning to free him at all costs, even if the price involves the lives of court personnel when Wilson goes to trial.

Lt. Harrelson and convicted dope dealer Johnny Rizi (played by Frank Gorshin) are stranded in very rough and remote terrain when the syndicate sabotages the helicopter in which Harrelson is transporting Rizi to jail. The Lieutenant is able to radio in their approximate location just prior to the radio dying, and the S.W.A.T. team and the syndicate racing to find the two, albeit with very different motives.

Lt. Harrelson and his team are assigned to handle security for General James Woodward (played by John Dehner), a World War II hero who now leads a racist paramilitary group.

Prosecutor John Stevens (played by Ed Gilbert) holds secret information which could convict two syndicate chieftains of capital crimes. Because Stevens insists on saying nothing until the grand jury convenes, and because police believe the mob has put out a major contract on Stevens, S.W.A.T. is assigned to protect him. However, the syndicate's enforcer plans to abduct the Stevens' daughter Tory (played by Jane Alice Brandon) and keep the girl until the father turns over the evidence. Oblivious to the danger, Tory is out for kicks as both the police and the syndicate to track her down.

A group of men steal a tugboat and barge laden with twelve cases of TNT, killing the tugboat captain in the process. They later threaten to blow up a Nobel Prize–winning marine biologist and her research vessel unless they are given one million dollars.

Marco, an arsonist-killer posing as a fireman (played by Peter Breck), engineers a fire during Southern California's dry season in the area's most affluent neighborhood, Sherwood Heights. While looting the evacuated home of a wealthy couple, one of Marco's men shoots a fireman. When S.W.A.T. is called in to locate the sniper, McCabe (James Coleman) is shot and gravely wounded. S.W.A.T. kills one of the snipers, but Marco and the rest of his gang escape with a truckload of stolen merchandise.

Lt. Harrelson's old friend, millionaire Doris Wainwright Bristol (played by Anne Francis), has brought expensive jewelry into the hospital where she is undergoing cosmetic surgery. Her bodyguard, Joe DeLeon (Frank Campanella), is slain after he spots criminal Frank Malloy (Michael Callan) posing as a dying patient; all part of a plot to steal Doris' jewelry. The S.W.A.T. team, who along with Hilda (Rose Marie) are at the hospital preparing for the children's Christmas party, find themselves forced into action when the discovery of DeLeon's body leaves Doris unprotected.

David Neal (played by Stuart Whitman), a government agent who spent four years on an undercover assignment posing as a crime boss's lieutenant, is marked for death after his testimony sends the kingpin to prison for life. After the trial, a $500,000 bounty is put on the head of Neal, who begins a new life in a small town as Ben Jordan. However, his police instincts come to the fore and he soon finds himself embroiled in another battle with organized crime.

Lt. Harrelson and his team are called to investigate two robberies in which powerful drills, cutting equipment and dynamite are stolen. During the investigation, Luca (Mark Shera) sets up a double date for himself and McCabe (James Coleman) with Sharon Merlingdale (played by Monie Ellis), a witness from another case and a student at a prestigious all-girls school, and a classmate. The thieves, who are planning to use the school as an entry point to a bank vault across the street, were counting on the school being empty for the weekend. When the girls agree to stay the weekend for their dates, they unwittingly place themselves and Luca in grave danger.

Bud Haskins (played by Eric Boles), whose father John is moving large quantities of unmarked automatic weapons as part of his warehouse operation, agrees to help three men crack open the safe in the elder Haskins' warehouse. Bud has had a falling out with his father and wishes to steal some of the money in the safe. When the thieves attempt to steal some of the weapons, Bud is killed trying to stop them. While S.W.A.T. is assigned to investigate the burglary-murder as part of their ongoing effort to locate the source of the weapons, John Haskins (Mark Stevens) recruits his Eastern mob partners to find his son's killers.

Lt. Eddie Chew (played by James Shigeta) is assigned to aid Lt. Harrelson when an elderly shop owner is beaten by an undocumented Chinese immigrant working as a shakedown man for Ronald Parker (played by Joel Fabiani); Parker is the Caucasian leader of what appears to be an all-Asian crime syndicate engaged in a protection ring. Lt. Harrelson begins to doubt Chew's integrity when it becomes obvious that the Chinatown criminals are being given secrets of his investigation.

Lt. Harrelson and his team are pursuing a group of men who are terrorizing the entire area by committing a series of rapes. The only clues are a religious medal found at one of the abduction scenes and a Biblical quotation overheard by one of the victims.

A group of militants take over a radio station and demand their jailed leader be released or they'll blow the station, along with their three hostages.

A mentally unbalanced veteran who has escaped from a psychiatric hospital is touring a movie studio, when he suddenly thinks he is back fighting in Vietnam. He takes two people hostage, leaving S.W.A.T with the task of disarming him.

After being severely wounded in an operation, Lt. Harrelson fights for his life during a lengthy brain surgery. While waiting at the hospital, the four team members reminisce about their best moments with the Lieutenant (in clips from previous episodes).

Luca (Mark Shera) is charged with manslaughter after he is forced to kill a man who was holding his own wife hostage at gunpoint.