Joe Mannix is visited one night by Ken Gordon, a young police officer whose life Mannix once saved. Unfortunately, moments later Gordon takes a bullet meant for Mannix, fired by Victor Roarke, a criminal whom Mannix once helped capture. Roarke is taken into custody, but claims to know the location of a missing judge's body -- but Mannix and Art Malcolm soon discover that Roarke's claim is part of an elaborate attempt at escape and extortion.
A former priest named James Conway comes to see Joe Mannix because he believes someone is trying to kill him. Conway has concluded that a former penitent, who confessed to a murder, believes that his confession is no longer safe because Conway has left the priesthood. Mannix accepts the case, hoping to find the man and convince him that his secret is safe with Conway. But then Mannix is disturbed to find that someone seems to be trying to kill him, too.
Mannix is hired by attorney Noah Otway to find out why someone tried to kill Otway's client, Dr. Graham Aspinall, a renowned surgeon whose specialty is removing tumors that are otherwise believed to be inoperable. Despite the doctor's denials that anyone has a motive to kill him, Mannix comes to believe otherwise when he barely saves Aspinall from a second attempt on his life. And Mannix discovers that there are several people who might have a motive to kill Dr. Aspinall -- including the second-in-command at his medical institute; the boyfriend of one of Aspinall's ...
The wife of a wealthy industrialist disappears from their sailboat off the coast of Mexico, and he initially hires Mannix to learn how she disappeared (and partly because he knows that a husband is usually the primary suspect in the disappearance of a wife). Then his wife is found, apparently safe, in a small village in Mexico. But after she returns to California, Mannix -- with Art Malcolm's help -- learns some disturbing information about her past, which suggests that she might know more about her disappearance than she is willing to admit.
A Vietnam war hero who married into the family of an aircraft manufacturer is killed by a grenade tossed into an elevator just before the doors close. The elevator operator, Roy Elkins, survives, but while in a near-coma, he keeps murmuring what appears to be a woman's name, "Joyce." Because Joe Mannix is Elkins' friend, he decides to try to find out why someone nearly killed him -- beginning with an attempt to learn what Elkins means by the mysterious "Joyce."
Joe Mannix goes undercover by joining a New Orleans mob to learn the identity of another member of the organization who wants to turn state's evidence against the head mobster, Lytell. His task becomes complicated, however, when he begins a romance with a woman named Angela who is close to Lytell and may still be loyal to him -- and when he learns that there is an informer within New Orleans' law enforcement who has tipped Lytell that there is an informant in his organization, too.
A young man whom his associates know as Dan Turner arrives in Los Angeles, where he separates from them and boards a bus for Palmdale. There he finds his family, who know him as Alex Lachlan, an Army Ranger missing in Vietnam and presumed dead. Joe Mannix is asked to help unravel where he has been for two years or why he is carrying Turner's identification. Mannix uncovers evidence that Turner/Lachlan may have fallen in with some shady associates -- and there appear to be reasons why Lachlan's brother isn't happy he has returned, either.
A young boy approaches Joe Mannix and offers him $1.85 to try to find a stamp album that the boy says he lost at an amusement arcade. After some investigation, Mannix believes the album might have been found by a street artist nicknamed Gemini whose girlfriend says he suddenly disappeared after talking about an "inheritance". Mannix' theory that Gemini found the album seems to be confirmed when Gemini tries to sell one stamp to a dealer - except that the stamp turns out to be worth thousands of dollars.
Mannix goes to what he believes is a meeting with a new client, but is ambushed by a gunman who accuses him of working for Bruno Raphael, a former crime boss now exiled from the United States. While trying to figure out why someone thinks he is working for Raphael, Mannix meets with Raphael's granddaughter and her husband, who tell Mannix that someone has been shadowing them. Mannix soon learns that Raphael has indeed returned to the United States - and that he is caught between Raphael and his successor mobsters, any of whom might have a motive to kill Mannix.
Two crop-dusting pilots who worked for orange grower Clint Carpenter have vanished without a trace. Joe Mannix is asked by his former military buddy, Dave Winters, who runs the crop-dusting service, to help solve the mystery of their disappearance. Mannix returns to the California farmland of his youth posing as a new pilot, but soon finds himself in the middle of a feud between his client and the local Armenian farm workers - whose leader claims that he and his people were cheated out of the land Carpenter now cultivates.
Joe Mannix refers four cases to down-on-his-luck fellow private eye Jerry Henderson. But when Henderson is murdered, Mannix suspects that it was because of one of the four cases he referred -- an extortion case, a divorce involving infidelity, a drug overdose victim's father, and a man being pressured by a loan shark. Feeling responsible for Henderson's death, Mannix decides to look into each case himself to find out whether one of them resulted in his friend's death.
Mannix travels to northern California, where he's been hired by the sister of a young man who disputes the cause of her brother's death. The coroner's verdict was accidental death when the man fell from a gantry at a sand and gravel quarry while drunk. Mannix finds evidence that his death may not have been accidental, beginning with his discovery of rifle shell casings at the quarry. But his investigation is halted when he's jailed on trumped-up charges by two local deputies -- who clearly intend that Mannix never come up for a court hearing or get out of jail alive.
A woman is murdered on a street near Peggy's home, and Joe Mannix is the first one to reach the murder scene. Joe questions a neighbor in a nearby house, and concludes the man may have seen more than he will admit. Hired by the deceased woman's husband to try to find her killer, Joe pursues the case and uncovers evidence leading to the uncomfortable conclusion that the woman's killer might be the son of one of Peggy's old friends -- and that he might also be responsible for the disappearance of the witness.
The wife of a wealthy jet-setter is accused of murdering a philandering playboy on her husband's yacht, and the wealthy man hires Joe Mannix to investigate the crime, hoping he will turn up evidence to exculpate his wife. Mannix finds that there is no shortage of suspects who might have wanted the murdered man dead -- including his own client and his client's daughter. But when another suspect is killed, and two hoods show up threatening Mannix to get off the case, Mannix realizes that he may be investigating more than just a murder among the idle rich.
The head of an electronics firm arrives home to find his wife drowned at the bottom of their pool, just as one of his rising young associates flees the scene. It looks like an open-and-shut case to the police, but the missing man's girlfriend insists that he is innocent, and asks Mannix to find the man and assist him. Mannix reluctantly takes the case, but the mystery soon deepens as Mannix discovers that the man may have had other identities -- and secrets aplenty in his past.
When a prizefighter is gunned down during a match, the initial speculation is that he was punished for refusing to take a dive. But Joe Mannix, who happened to attend the match, speculates that the bullet may have been meant for someone in the audience -- and a review of the fight film suggests that the real target was Mannix himself. This is reinforced when there is another attempt on Mannix' life -- but the evidence begins to point to someone whom Mannix believes couldn't possibly have tried to commit the murder.
Joe Mannix is visited by Portia and Penelope Penhaven, two elderly, eccentric sisters who insist that Mannix investigate a hit-and-run earlier that day, which damaged one of the headlights on their ancient automobile. Amused by their request, and overborne by Portia's forceful personality, Mannix agrees to look into the matter, but discovers that the vehicle that hit them was taken from a rental lot, apparently without the knowledge of the lot's owner. Digging deeper, however, Mannix soon discovers that the hit-and-run might be related to a murder committed nor far ...
Against Joe's wishes, Peggy agrees to go undercover to gain evidence against a woman named Dodie Green, who is believed to be the source of heroin that caused the death of a teenager whom both Joe and Peggy knew. Peggy manages to work her way into Green's operation, but is unaware that the handsome man who starts to court her is actually working with Green - or that he seeking to prove that Peggy is a police informant.
A woman's body washes ashore, whom Lt. Art Malcolm recognizes her as Joe Mannix' former girlfriend, Carol Lockwood. The forensic evidence suggests that she was killed during a boat explosion, possibly while in the company of a wealthy man with whom she also had a relationship. But as Mannix examines the evidence, he begins to suspect that Carol's death was more than just an accident -- perhaps even part of a sophisticated murder plot.
Gil Ryan, a shady underworld figure, is the star witness in the criminal trial of Lucas Hume, a man with connections to city politics. Then Ryan is gunned down in spite of his police protection, and Hume is found standing over the body, holding the gun that fired the shots. Despite what appears to be an open-and-shut murder case, however, Joe Mannix is hired by Hume's sister, who claims to have had an affair with Ryan -- and wants Mannix to prove that she, not her brother, was the one who shot Ryan.
Joe Mannix is hired by wealthy businessman Adam Langer to dig up enough dirt on a politician to destroy the man's career. At first Mannix is unwilling to take the job, until Langer explains that that politician is himself -- that he wants to run for governor and needs to learn what a political opponent might be able to uncover. Mannix initially finds some mildly damaging information on Langer -- but becomes concerned as the witnesses he has interviewed start to meet violent deaths.
A hobo known as Boston comes to see Joe Mannix, explaining that someone has recently tried to kill him, and asking Mannix to find out who it is and why. Mannix agrees to look into the matter, and eventually realizes that the distinctive overcoat Boston wears might be what has made him a target -- because he "inherited" the coat from another hobo who might have overheard something about an underworld killing.
William Avery is released after serving a prison sentence for embezzlement, but almost immediately dies in a car accident. Someone nevertheless begins to stalk his daughter, apparently believing that she knows where the missing money is hidden. Though Avery's daughter insists that her father was innocent, she hires Joe Mannix to protect her -- and Mannix concludes that the best way to help her is to re-open an investigation of the theft, to find out who from Avery's past would still want to find the missing funds.
Joe Mannix is invited to the home of Arthur Danford by an old friend, Barney Edmonds, who is managing Danford's campaign for governor of Hawaii. Mannix recognizes Danford's wife, Laura, as a woman who once had a shady past, which put her on the fringes of a mob killing. Laura confides to Mannix that she is being blackmailed by her old boyfriend, who is threatening to reveal her past life to destroy her husband's political career. Mannix offers to intercede with the blackmailer -- but as he tries to find the blackmailer, each person Mannix locates seems to meet with ...