Lt. Frank Ballinger is a no-nonsense plain clothes cop in the elite M Squad Division. The Squad's task is to root out organised crime and corruption in America's Second City, Chicago.
Episode 1
The Squad is on the lookout for a bank robbery suspect with a unique feature, witnesses say he has gold teeth.
Episode 2
Ballinger and the Squad are out to catch a burglar who may have rabies.
Episode 3
The squad hunts down a cop killer.
Episode 4
The squad goes after a jail inmate who's just escaped.
Episode 5
Ballinger investigates the murders of four women. The victims were all connected to the same church and lived within two miles of each other.
Episode 6
Chicago cop Frank Ballinger stages a rescue in order to gain the confidence of Alice, a young woman who works for suspected jewelry fence Louis Prince. Pretending to be furniture salesman Bob Steele, Ballinger romances Alice and gets friendly with her boss. But Alice falls for "Bob" and Ballinger must weigh her feelings and safety against his duty as a police officer.
Episode 7
Lt. Frank Ballinger investigates the case of a gambling ring and its connection to an unidentified police officer. The deeper into the investigation he gets, the more Ballinger becomes concerned that the crooked cop may be an old friend.
Episode 8
A jewelry store robbery sends the thief to prison, but his claim that the night watchman, a former big-league ballplayer named Lightnin' Joe Adams, was in on the heist costs Adams his job. Lt. Frank Ballinger goes undercover in prison to find out from the robber whether Adams was involved in the crime and what happened to the loot.
Episode 9
Frank Ballinger and his colleagues on the M Squad have to find a needle in a haystack: a cop killer somewhere in the city of Chicago. Their only clues are an old magazine and the killer's habit of saying "You bet."
Episode 10
Lt. Frank Ballinger keeps an eye on Hazel, a bar girl with a record who nonetheless wants to go straight. He discovers she is involved with Joe Mazzerin, a safecracker. Ballinger goes undercover to get the goods on Mazzerin and to learn who his mysterious partner is.
Episode 11
When perennial loser Wally Gardner is identified as the perpetrator of a robbery-murder, he tells police unique details of a stranger he met miles away at the time of the crime. But when that stranger is found, he says he can prove that HE was miles from where Gardner says they met at the time of the crime. Lt. Frank Ballinger must determine who's lying.
Episode 12
When a hired gunman gets himself tossed in jail following a fistfight, Lt. Frank Ballinger takes his place undercover as protection for a group of three businessmen who meet once a year to commit a specialized crime.
Episode 13
When his partner in an investigation is killed, Lt. Frank Ballinger makes it a personal business to pin the crime on narcotics lord Sam Hinder. But, as Ballinger discovers, Hinder has an unusual reason for wanting to keep the police out of his own personal business.
Episode 14
Gangster Tommy Hatch is wanted for murder, but the police have to keep him safe from other gangsters who want him dead before he can testify against them. Lt. Frank Ballinger is assigned to protect Hatch even though he despises him.
Episode 15
Ballinger investigates the case of a security courier who is charged with robbing himself of $75,000.
Episode 16
District Attorney Grover calls for Ballinger to help him sort out a potentially embarrassing situation involving the murder of a former business associate.
Episode 17
The room mate of the third murder victim of the Blue Indigo serial killer may be the only link Ballinger has to catching him.
Episode 18
When a convicted murderer gets the upper hand on Lieutenant Ballinger during a train ride back to Chicago, his last best hope for recapturing the felon is the persistence of an alert young boy.
Episode 19
Ballinger suspects an inside job when a dry cleaning company refuses to knuckle under to a shakedown mob.
Episode 20
Kathy Bane, an old flame of Ballinger's, needs his help when a blackmailer trying to extort money turns up dead-- in her apartment.
Episode 21
Ballinger investigates a murder with multiple motives.
Episode 22
A man's aunt reports her nephew is missing. Ballinger investigates.
Episode 23
Ballinger goes undercover to capture a robbery suspect.
Episode 24
Ballinger investigates after a bank robber leaves a pencil at the scene.
Episode 25
A woman dies. Ballinger investigates.
Episode 26
A woman loses her memory. Bellinger investigates.
Episode 27
Bank robbers hide in a suburban house.
Episode 28
A sniper is terrorizing Chicago. Ballinger joins the hunt.
Episode 29
A young wife is shot by an unknown assailant when she drives with her ex-con husband to an isolated woods in search of their dream home. No one even reports the couple missing until after the police find them dead in the snow. The wife's sister is a wealthy spinster, who takes her time even coming to Chicago, claiming her brother-in-law was threatened with death by a blackmailer. Det. Ballinger suspects the sister knows more than she reveals.
Episode 30
A boxer's (Lancaster) life is being threatened soon after another fighter dies after fighting with Lancaster. Suspicion falls on the other fighter's trainer who feels Lancaster is responsible for the death of the other fighter.
Episode 31
A man confesses to a crime he may not have committed. Meanwhile the president of the company where the man works has been shot to death.
Episode 32
Lieutenant Ballinger searches for a mentally ill young woman who shot a psychiatrist, hoping all the while that he can also find sufficient evidence to obtain a felony conviction against the charlatan who was "treating" her.
Episode 33
Frank Ballinger investigates a illegal adoption racket.
Episode 34
Ballinger investigates a rash of counterfeit $20 bills.
Episode 35
A professional man is identified as a jewelry-store robber, threatening his freedom, not to mention his wife's reputation "from being married unknowingly to such a character". Ballinger investigates.
Episode 36
An illegal roving casino eludes the police and cheats players with crooked games. When Ballinger investigates, he encounters additional, unforeseen threats.
Episode 37
No overview available.
Episode 38
A millionaire is found dead in a locked room. His young pretty wife (Fay Spain), and the big hansom driver (Ken Clark), are suspected of the crime. Lee Marvin figures out how the crime was committed.
