Lt. Frank Ballinger investigates the latest in a series of murders of women. Eddie Ferguson, the husband of one of the most recent victim, claims he saw a face outside his window upon discovering his wife's body. But Ballinger begins to suspect that the distraught, church-going Ferguson may have dark secrets.
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.
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.
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.
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."
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.
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.
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.
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.
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.
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.
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.