Joe Mannix is asked by his old friend, Mildred Oliver, to look into the circumstances of her daughter Leslie, who has become an alcoholic and has been acting strangely lately. In the middle of his investigation, Leslie becomes a suspect in the murder of an unemployed trumpet player, who appears to have been blackmailing Leslie and receiving payoffs - which gives her the perfect motive to have killed him.
Joe Mannix is on a ski vacation to the Sierras where be becomes acquainted with two young women, Barbara and Marie. Barbara disappears on the slopes, and is later found dead after an apparent ski accident. But then Mannix learns that Barbara and Marie had switched ski outfits, making it easy to confuse one for the other on the ski runs. He begins to suspect that Barbara's death may have been to cover up an attempt on Marie's life, or an attempt to kidnap Marie -- especially when someone tries to kill him as well.
Mannix is jogging on a beach near an isolated point of land overlooked by a large house when he witnesses a woman being dragged inside the house by two rough-looking characters. He has a neighbor call the police, and when the sheriff's deputy arrives, Mannix describes the two men and the woman he saw being attacked. He is startled, however, when the deputy tells him that his description of the crime and of the three participants perfectly matches the murder of a woman in that house - except that it happened a year before.
Joe Mannix once again returns to his hometown in California's Central Valley, this time to assist Armenian attorney Leo Kolligan in defending Juan Esparza, a farmworker accused of murder. Esparza is a labor organizer who organized picketing against Charlie Apellini, the owner of the vineyard where the victim worked. In between stints of working on the case, Joe finds time to reconnect with his father, Stefan -- who is much more accepting of Joe and his chosen profession than he was during Joe's visit two years before.
Joe Mannix is approached one evening by a woman named Lisa Ralph, who says that she believes someone may be trying to kill her, possibly because she has a valuable manuscript that she inherited from her late father. Mannix agrees to help her, but begins to have his doubts about her when she first disappears from his office, and then later leaves him at a restaurant without explanation.
A woman hires Joe Mannix to find her missing brother, whom she says is an alcoholic living on skid row. Mannix locates the man, but finds that he is not the woman's brother -- although he is the target of several hoods who want to kill him. As he pursues the case, Mannix learns that the man may actually be an investigative journalist who was on the verge of breaking a major story when he disappeared under mysterious circumstances.
A group of boys who play baseball together hire Joe Mannix to look for their coach, who has gone missing shortly before an important game. Mannix discovers that the man was actually an ex-con who changed his name as soon as he was released, and failed to keep even one appointment with his parole officer. Mannix begins to believe that the man's disappearance may be explained by the number of other criminals who seem determined to locate him -- possibly to silence him for good.
Joe Mannix and Peggy go to a nightclub intending to listen to a young guitarist, where Peggy recognizes a fugitive criminal named Brastow. Joe manages to recapture Brastow, who is to be extradited to New York to face charges of murdering a police officer. Brastow is to be escorted by an old acquaintance of Joe's named Ross Santini, now a New York detective. But Joe becomes puzzled by several attempts on his life by men he believes to be working for Brastow, and concerned about his friend Santini's increasingly odd behavior.
On a rainy day in Los Angeles, Joe Mannix' secretary Peggy is kidnapped by two men on the instructions of crime boss Lawrence Powers. Powers has the two men hold Peggy to force Mannix to investigate which of his three closest associates is acting as a stool pigeon. Mannix only has 72 hours to learn this information -- or Peggy's life will be forfeited.
Joe Mannix is summoned to a scene where an old friend of his, Monte Dawes, has killed one man and is holding a young woman, Cindy Warren, hostage. His friend is killed, and Mannix manages to overhear his dying words, which seem to make no sense - something about a "button" and a "General D." With the help of Cindy Warren, to whom Mannix feels an increasing attraction, he tries to puzzle out why Dawes ended up dying as he did - and why several hoods seem to be interested in him and Miss Warren.
Late one night, Joe Mannix is surprised by Gen. Alec Holt, his former commanding officer in Korea, now a good friend and vice-president of Coronet Electronics. He tells Mannix that he is being blackmailed by a photographer who has pictures of him in a compromising position, and gives Mannix $10,000 to buy the film. Mannix makes the exchange but then is jumped by two thugs. Although he manages to escape, a return visit from the two thugs and Gen. Holt's refusal to explain why the two men want the film leads Mannix to believe that the case involves more than evidence of...
While visiting a rural property to investigate a case, Mannix is attacked by two bikers and nearly killed. He concludes that someone wants to scare him off of one of the three cases he is currently working on - wealthy parents who are searching for their missing daughter; an embezzlement case for a fellow private detective named Dan Brockway; and a threatening telephone call received by a young couple. But as soon as Mannix decides to figure out which case prompted the warning, he learns that he has been fired from all three cases at the same time.
Tip Ellis, a fellow private investigator and friend of Joe Mannix, is murdered while looking into a case of industrial espionage in Fresno. Mannix travels to Fresno to pay his respects, and also to look into the case his late friend was handling. In the meantime, a letter postmarked from Fresno arrives at Mannix' office -- possibly an effort by Tip Ellis to pass along information about the case to Mannix. That letter begins to take on great importance when someone takes extraordinary measures to steal the letter from Mannix' safe before he can read it.
A dying man stumbles into a church and tells a young nun that he was responsible for sending an innocent man to prison. Her parish priest asks Joe Mannix, an old friend, to find out who the dead man was referring to. Mannix discovers that the dead man was a witness in a murder trial several years before -- but the man in prison, and his former attorney, steadfastly insist he was guilty. Mannix reluctantly begins to accept this, too -- until several attempts are made to convince him to stop investigating the case.
Fellow private investigator Charlie Frome is killed by a hit-and-run driver, apparently while working on a case, and Joe Mannix decides to see if he can determine why Frome was murdered. He learns that Frome was working for television star Danny Brite, but Brite claims he hired Frome only to look for a former acquaintance. Based on evidence found in Charlie Frome's apartment, however, Mannix concludes that Frome's investigation involved a soldier in Vietnam who has gone missing in action -- and possibly someone who is blackmailing Danny Brite.
A maverick computer genius named Bobby Quinn is gunned down by a sniper while playing golf with his employer, Lawrence Martin, the head of a large conglomerate. Martin hires Mannix to find the plans for a revolutionary computer that Quinn designed that will be the size of a briefcase. What Martin doesn't tell Mannix is that he knows Quinn also left behind a letter with the plans that has damaging information against Martin -- and that Martin has taken steps to ensure that Mannix will never read the letter even if he locates the plans.
Mannix is hired by a woman from Cleveland named Marcia Inman to locate her missing husband. Mannix investigates her husband's business contacts and follows a man matching his description after the man leaves what appears to be his mistress' apartment. But when the man Mannix followed ends up dead, Mrs. Inman claims that the dead man was not her missing husband.
Someone tries to kill Ken Mitchell, the head of a toy-making firm. Not wanting a violent incident to be associated with a toy business, Mitchell instead hires Joe Mannix to find out who might have tried to kill him. Suspicion soon falls upon Mitchell's "silent partner," Paul Anders, but Mannix' investigation is stymied when it first appears that Anders may have committed suicide . . . or may never have existed.
Tom Fortune, the rising young scion of a mobster family, tries to hire Mannix to shadow his wife, whom he suspects of being unfaithful, when Fortune is gunned down. Fortune's family members, especially his father, suspect that Mannix set up Tom for the ambush -- suspicions that are enhanced when Tom Fortune's widow is spotted leaving Mannix' office.
A man named Tom Farnon suspects his wife of having an affair, and follows her to his boat where she is to meet her lover. But a shot rings out, the other man flees, the boat explodes, and Farnon finds himself a suspect in her murder. Farnon approaches Joe Mannix and asks Mannix to learn the identity of the man she met. The best lead Mannix has is Phil Rand, another private investigator who once worked for Farnon -- but Rand insists that Mrs. Farnon never had an affair.
Vince Logan is a talented singer who is also a friend of Peggy's. One night while he and Peggy are in a nightclub, Logan is approached by a police officer about what appears to be a minor property damage claim. Logan responds by taking a gun and barricading himself in a warehouse, where he eventually is shot trying to flee. As Logan fights for his life, Joe Mannix decides to try to find out why Logan was so reluctant to cooperate with the police even about a routine matter.
Police Lt. Larry Gifford follows a tip leading him to a warehouse, where he surprises a man apparently committing a burglary. After an exchange of gunfire, Gifford discovers that the man he killed is Danny Constantine, who once killed Gifford's partner but was released on a technicality. Facing possible dismissal from the police force, or even murder charges, Gifford hires Joe Mannix to try to find information that will clear his name.
Joe Mannix is called to the office of an air freight company and asked to investigate some cargo thefts, unaware that this is a ruse to allow the operators of the company to substitute a double in his place. When Mannix then tries to leave on a confidential trip to London, he is kidnapped by the men from the air freight company and taken to a remote old west ghost town - while the impostor takes his place on the mission to London.
Joe Mannix is participating in an auto race when he suddenly begins to experience hallucinations. The resulting crash lands him in a private hospital, where the delusions and paranoia continue. But then a young nurse confides in Mannix that the physician in charge of the facility -- whom Mannix also knew as his friend -- has actually been giving him drugs to keep him in that condition. With her help, Mannix arranges an escape, to learn why he has been victimized in this way.