The niece of Ray Endicott, one of the soldiers from Joe Mannix' old unit in Korea, is murdered in her apartment, and a lighter found there links the killing to another member of the unit, Tommy Gantt, who once dated the girl. But Mannix isn't convinced of Gantt's guilt, and begins to believe that the real killer is yet another former member of the unit -- who may be taking revenge on his former comrades one by one.
On his way to visit a potential client in an office building late at night, Mannix surprises a burglar in a jewelry store. The burglar is killed in a shootout, but the police investigation suggests not only that Mannix did not kill the man in self-defense, but that he stole some of the jewelry. With his license suspended and his finances dwindling, Mannix is tempted to accept an offer to be the bodyguard of a reputed mobster's widow.
Sonny Carter, once a world-champion boxer, has been accused of killing a man who sometimes hung around the boxing arenas trying to fix fights. Sonny's aunt calls her old friend, Peggy, to ask if Joe Mannix will try to find Sonny, who has disappeared. Mannix agrees to look into the matter, but he gets attacked by some thugs who tell him to stop his investigation. The other problem for Mannix is Sonny himself, who would rather flee than face the police investigation.
Someone has been making threatening telephone calls to Joe Mannix, and this mysterious person begins to take shots at him, too -- one of which cuts down Joe's friend Barry Nolan, who runs the photography shop across from Joe's office. That incident brings Joe into a chance encounter with renowned magazine photographer Jill Packard, who eventually begins a friendship with him. But Joe begins to suspect that there's more to the threats than someone who just has a grudge against him, when one of the shots nearly hits Jill, too.
Mannix is hired by the sister of Geoffrey Paradine, a college student who has disappeared. As the episode opens, Mannix is taken off the case because she claims to have found him. Then she admits that although Paradine has contacted her, she believes that her brother is still in trouble. But as he continues to search for Paradine, Mannix starts to have strange hallucinations -- the first symptoms that someone has poisoned Mannix with a slow-acting toxin that will eventually kill him unless an antidote can be found.
A group of prisoners on death row in a prison near Lawson City stage a takeover, taking as a hostage a guard named Charlie Keefer, who is a friend of Joe Mannix. The prisoners demand that Mannix come to see them, where they tell Mannix that one of their number, Carl Dancik, is innocent, and that they want Mannix to re-open his case. Dancik was convicted of the murder of an old girlfriend, but claims he was framed for the crime. With only a few days to turn something up, Mannix turns to another old friend in Lawson City, award-winning newspaperman Frank McGill, to see ...
Victor Brady, a leader in the electronics business, runs up a gambling debt of nearly $250,000 to a Las Vegas casino. Brady's private plane disappears from the radar on its way back to Los Angeles, but after his memorial service, his widow hires Joe Mannix to look for him, claiming that her husband is still alive and contacting her for help in raising the money to pay the casino. His investigation leads Mannix to that casino and the assorted people who work for it and who knew Victor Brady.
Peggy is shot by a stray bullet when Joe grapples with a gunman who has come to the office to steal evidence from one of Joe's cases. While she recuperates in the hospital, she finds herself strongly attracted to the patient across the hall, who is staying in the hospital under an assumed name. She eventually discovers that he is the seriously ill head of a recently-independent African country -- and that the reason for his being incognito is that his political enemies hope that he will not survive his medical treatment.
Mannix is on his way to go fishing in the desert when he stops at a roadside diner for gas and a check of his engine. While having a cup of coffee, he discovers that the couple who run the diner are being held hostage by three men. Mannix manages to reach the authorities -- but the mystery deepens when the couple claim to know nothing of their supposed kidnapping.
Joe Mannix is about to go on a golf date with his friend Pete Pinelli, a helicopter traffic reporter for a local radio station, when he receives word that Pinelli's copter has crashed in a remote area of Los Angeles County. Mannix uncovers a witness who saw a light plane in the area just before the crash, and becomes convinced that Pinelli was murdered because he saw something that he wasn't supposed to see -- a conclusion that's bolstered when the pilot of the light plane appears to have been murdered as well.
While playing in an abandoned movie theatre, a nine year-old girl observes three men watching a film and overhears them apparently plotting to kill someone. The girl's mother takes her to see Joe Mannix, who is initially skeptical because the girl sometimes seems to confuse reality and fantasy. But Mannix starts to believe her story when an attempt is made on the girl's life.
A young woman visits Joe Mannix at his office with a strange story of having had a dream in which he was killed. Mannix reassures her that he doesn't see any danger, and suggests that she dreamed about him because his capturing a blackmailer was recently covered in the newspaper. But Mannix begins to have second thoughts about dismissing her story when the details of her prediction come true.
Joe Mannix is hired by Ellen Gray, whose husband committed suicide in Hong Kong shortly after confessing that he was apparently in over his head in some shady business dealings. When Ellen returns to Los Angeles, however, she finds herself being shadowed by some mysterious men who also had followed her in Hong Kong -- and whom she fears now may be trying to kill her.
A client named George Hewitt hires Joe Mannix to help find a man whom Hewitt claims has been harassing his wife, such as by accosting her in a taxicab in Chicago. Hewitt then speeds off from their meeting and is killed in a car chase with another vehicle. Mannix tries to discuss Hewitt's concerns with his widow only to find that she denies many of the things Hewitt had told Mannix -- such as never having been in Chicago, and not recognizing the man from a photograph.
After leaping from a bridge to escape two hoodlums who were trying to run him down, Joe Mannix awakens in a hospital on a Monday morning with no memory of the previous 24 hours. With Peggy's help, and a few clues from items in his possession when he was found, Mannix begins to reconstruct the missing Sunday as fragments of his memories return -- including time spent with a beautiful redhead, and the image of a young woman falling from a high place.
The police chief in a small town 100 miles north of Los Angeles asks Joe Mannix to come to the town to assist him. Another old friend of Joe's, Paul Parrish, whom Joe convinced the chief to hire after Parrish had been in prison for a crime he didn't commit, is now suspected of killing his former cell mate from San Quentin and stealing $150,000 in cash that the cell mate had hidden before going to prison.
Tough L.A. police Lt. Ira Deegan is warned off the investigation of a heist that netted $85,000 -- a threat that seems to have come true when his garage is blown up, although no one is hurt. Then Joe Mannix begins investigating the theft, which he claims is for the $8,500 recovery fee offered by the insurance company that would have to pay off on the theft. But Mannix' client is actually someone who is worried about Deegan's safety -- namely, his wife.
A young boy named Dennis Coverly comes to Joe Mannix and tries to hire him. The boy says his parents have been arguing about whether to go to the police about something that happened the previous Saturday night when they were at a restaurant celebrating their anniversary. Mannix visits the boy's parents and is assured that nothing is wrong -- but Mannix starts to have second thoughts when he notices a former felon watching their house, and shortly thereafter someone tries to kill Mannix when he visits the restaurant.
Mannix travels to a western ghost town in response to an urgent telegram, only to learn that he's been lured there by four surviving members of his undefeated college football team, along with two of their wives, for an impromptu reunion. But then one of their number is killed, and Mannix discovers that their means of leaving the town has been sabotaged, too -- meaning that someone, perhaps the absent member of the team, intends to kill them all.
Joe Mannix is hired by a secretive businessman named Alton K. Moore, who wants Mannix to look for his son Cal, a college basketball player who has been missing for several days. Although the case takes Mannix back to his alma mater, he has his doubts about Moore, who insists on meeting in remote places instead of at his office. His concerns about the elder Moore -- and the serious trouble that Cal may be in -- begin to seem justified when several thugs begin shadowing Mannix during his search.
Mannix is summoned to the apartment of Dorothy Kinman, a former Olympic-class diver who was rendered a paraplegic in an auto accident. Besides being reluctant ever to leave her apartment, Ms. Kinman claims that a man keeps telephoning her with death threats. But although he's initially concerned for her safety, Mannix begins to suspect that the threatening phone calls may just be an illusion -- or a hoax -- on Ms. Kinman's part.
A somewhat ditsy heiress named Cindy Conrad comes by Mannix' office one evening, complaining that a mysterious woman has been phoning her to offer important information about the death of Conrad's father several years before. Mannix correctly guesses that the caller wants a large sum of money to provide the information. He tries to convince Conrad to ignore the calls -- but he begins to believe that something is wrong when someone takes a shot at them as he is escorting Conrad to her car.
Joe Mannix receives an urgent letter from a woman named Lynn Sargent asking him to fly to Arizona. She meets him at the airport and hands him a check for $1,000 and a small sealed package, telling him the money is his fee to take the package to the Los Angeles Police Department. Just as she does so, two men try to take the package, but Mannix manages to retain it after a scuffle. But the mystery deepens when the package turns out to contain nothing but blank sheets of paper -- and the police chief in the town tells Mannix that Lynn Sargent died a month earlier in a ...
A serial killer who calls himself "Overkill" has been terrorizing Los Angeles, and the most recent victim was "Red" Bailey, an old friend of Joe Mannix. But as Mannix and the police look into Bailey's killing, they learn that Bailey was investigating the Overkill case on his own -- and may have discovered that at least one of the killings attributed to Overkill was a copycat murder that someone wanted to be blamed on Overkill.