Student activists protesting for academic changes at their college take over the administrative building, and hold Julie and an elderly and ill female teacher hostage. Meanwhile, a seemingly quiet but demented student named Walter has taken their otherwise peaceful fight into fanatical-warlike territory with a rifle and other weapons! It's up to both the men of Mod Squad and the hostages to stop Walter before he kills any more innocent people.
In a reversal of the more common situation, a conventional young friend of Julie's asks the trio's help in locating her father, who has gone into the hippie subculture. Unknown to any of them, he has also unwittingly become involved in a girl's murder, which the trio is also trying to solve.
A businessman reports the theft of his partner's car---and admits that he wired it with dynamite, set to go off in eight hours. Unfortunately, the search for the car is complicated, as the thieves change the plates, and the car changes drivers more than once.
A straight-laced young minister comes to L.A. to investigate the murder of his brother, a doctor who had set up an inner city free clinic for homeless and runaway youths. Many stolen goods were found in the doctor's clinic after his murder, and no one, including Pete, Linc, and Julie as well as the brother, believe he could have been involved in burglary. Linc is assigned to go undercover and accompany the minister in his search for answers.
Greer and another veteran cop have both been frustrated by a drug pusher they've been trying to nail, who has twice had his case dismissed on legal technicalities. Finally, the third time appears to be the clincher, as the man is caught at an airport with a case full of heroin. But then the pusher calls Greer to his cell and insists that he has been framed, and Greer reluctantly agrees that something about the case doesn't fit.
A girl working undercover for a cop trying to bring down a drug lord is accidentally killed. Because of her resemblance to the dead girl, Julie is quickly recruited to impersonate her and continue in the mission, despite the great risk.
The trio tries to help a boy in his search for his father, who came to L.A. from West Virginia hoping to find work. It soon becomes apparent that there are people who don't want them to find the man, and that he is in debt to loan sharks.
A middle-aged legendary prizefighter tries for a comeback match, mainly to please his troubled son, whom he thinks wants him to prove he's not a has-been. But the son may have other reasons: he is in debt to gamblers who want him to give them inside information on his dad's odds. Linc feels that the fighter may be in physical danger if he goes ahead with the match.
While working undercover as safe crackers, Pete and Linc meet a timid, clumsy young man who asks them to teach him about their trade. They learn that the young man has a twin brother who is a successful businessman. What they don't know is that the businessman is actually the leader of the industrial spying ring they are trying to investigate. And that's only the start of the surprises to come.
When his motorcycle breaks down on a trip, Linc stops in an abandoned town, only to discover that a kidnapped boy is being held there for ransom. The kidnappers decide to hold Linc as well until they get the money.
After Captain Greer shoots and kills a young man in self defense during a bust, he suffers from feelings of guilt and remorse. Julie suggests he take a vacation at a secluded resort to sort things out.