In the series debut, individualist private detective Joe Mannix is working at a corporate agency. Company rules dictate only one piece of paper on a desk at a time; Mannix's desk is cluttered. Despite Mannix's disdain for the rules, the head of the agency, Lew Wickersham also knows Mannix "is my best man." Mannix is sent to investigate a missing person's case. The client is a retired mobster, who first tests Mannix. The detective is told the missing person, the mobster's daughter, is kidnapped. Mannix will encounter much treachery before learning the true facts of the...
A potential candidate for governor, a successful businessman employs Intertect to probe his background. His rationale: he wants to see if the detective agency can turn up any dirt that could be used by political opponents. If Intertect can't find any, he reasons his political opponents wouldn't be able to do so, either. Mannix follows his own leads while his Intertect colleagues probe the obvious. As Mannix's investigation progresses, people he has interviewed turn up dead. It turns out the candidate is part of the Syndicate and even sits on its council. Now, Mannix ...
A group of businessmen approach Intertect. They say they want to approach a former colleague and offer him $1 million for a new formula. Mannix is suspicious the clients aren't telling the truth. He befriends the daughter of the man the businessmen want to approach and she falls for him. Mannix keeps digging and discovers the clients are really Nazi hunters. Or are they really Nazis? Mannix must find the answer and save the life of the daughter.
A little girl wishes to "rent a detective" to prove that her father, who is on Death Row, is innocent. Mannix takes the case, working on his own time, and will have to do without Intertect's help. Mannix romances the mistress of a reclusive rich man at whose estate the murder took place. The detective must cope with a web of deceit to find out what really happened.
A model spots a Latin man she met on a vacation but he flees. She hires a former boyfriend, Joe Mannix, to track down the man. But the case quickly becomes more complicated. It turns out the Latin man is an assassin. The lives of both Mannix and his client are now endangered.
Mannix is hired by an old friend to find his college-age daughter, who is living in a commune. Mannix soon discovers the commune has secrets that can be deadly to discover. One college basketball player has already died. And why is a hoodlum so interested in what transpires at the commune?
A 26-year-old woman, worth $10 million, hires Intertect to do a background check on her boyfriend. It turns out the woman has spent 10 years in a mental hospital and seems on the verge of cracking up. Mannix suspects something more sinister. The woman is surrounded by shady characters. The detective concludes one of them seeks to drive her back to the mental hospital.
Mannix, on the mend after a gunshot has one foot in a cast, is given a routine assignment by Intertect boss Lew Wickersham: get the signature of a man named Amos Silo on a legal document. The detective takes a bus to a small town but finds a chilly reception whenever he inquires about the man or his ranch. The town is hiding something. As Mannix digs deeper, he discovers dead cattle are part of the mystery. The question is whether he'll survive to find out the rest.
Mannix is working on a child custody case that should be routine. It isn't. It begins with Mannix barely saving the life of the boy who is the subject of the custody fight. As Mannix's investigation continues, it becomes clear the boy's father is the target of killers, including one attempt by using explosives. Yet, the father isn't rich. Mannix must figure out the motive before the boy and father are harmed.
A burglar steals notebooks from a psychiatrist but double crosses an accomplice and takes the notebooks for himself. One of the patients hires Mannix and Intertect after being blackmailed. Mannix's client is a movie studio art director who has a secret in his past. The trail turns deadly. The burglar and a companion turn up dead and Intertect boss Lew Wickersham is wounded.
A crusading newspaper editor is preparing an explosive expose of a state legislator. But a man who supposedly had the documentation has fled just as the story went to press. The editor hires Intertect, which sends Mannix to work on the case. Mannix and Intertect boss Wickersham come to doubt whether the legislator is corrupt. But somebody is responsible for a trail of bodies and Mannix is determined to find out who.
Intertect is retained by the police department to help transport a woman informant to safety. At least that's the story Mannix is told by a police inspector. But the case proves more complicated -- and very deadly. The informant turns out to be an undercover policewoman and Mannix is really a decoy. The policewoman is killed and Mannix remains the target of crooked cops.
Mannix infiltrates an alcohol-rehabilitation center in Mexico. His client is a young woman who fears her father is being swindled. Intertect has devised a cover identity so that Mannix poses as an alcoholic who has been committed there by an Intertect operative posing as his wife. Mannix discovers a confidence man is also posing as a patient. In the middle of the case, another patient turns up dead and Mannix finds out there have been several unsolved murders nearby. If Mannix isn't careful, he could be the next victim.