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.
M Squad hunts for a bomb before it blows up a hospital. Jonas Blecker, an embittered bank clerk who went to prison for dipping in the till to loan money to depositors down on their luck, wants to commemorate his 1st anniversary as a free man by killing the judge who gave him the maximum sentence. The judge is in Columbus Hospital for a delicate operation and he can't be moved.
Mrs Ashton is killed during a house robbery. The M squad are brought in to try and work out what happened. A very open and shut case suddenly becomes exceedingly complex.
When a well-liked retired couple is found brutally murdered, evidence points to their curmudgeonly neighbor. Lieutenant Ballinger is initially skeptical of his story, but thorough investigation reveals that things are not always as they seem.
The M squad is called in after a series of factory fires occur in the Chicago area. The case become complex after the unusual chemical signature of the fire accelerants is identified.
Detective Ballinger is brought in to investigate the murder of night club owner Joe Dalio. The case seems open and cut with a suspect in custody, however Ballinger has just enough doubt to continue the investigation.
A bail bondsman's son is kidnapped to force his father to post an $80,000 bond for the release of a murderous extortionist. Lieutenant Ballinger finds himself on a dangerous high-speed boat chase when the culprit attempts to avoid trial (and a likely death sentence) by escaping to Canada.
Detective Ballinger is called in after what seems to be a professional hit on a desk clerk at a hotel. A witness identifies who may have done the killing, but Ballinger is concerned he can not find any connection for why the clerk should have been shot.
Ballinger is called in to investigate when a burning car is found with the body of a young woman bound with wire inside. The chief suspect, playboy lawyer Paul Crater, seems to have an air tight alibi. Ballinger needs to cast his net wider to solve this mystery.
Used car salesman Larry Colman has argument with Art Brunswick, a man who claims to the be the father of Colman's daughter. Colman unearths evidence Brunswick is not who he claims to be leading to a deadly altercation.
Ballinger is part of an ongoing investigation into racketeering in the night club industry. After a fight breaks out in a club, Ballinger thinks he might have the break he has been looking for.
Harry Conklin is killed while on the way to a secret Senate hearing into stand over tactics in the trucking industry. Suspicion falls heavily on a rival Martin Bodie. It is up to Ballinger to fight through the silence and uncover the truth.
Danny Sutton is arrested. During the interview a rookie detective makes a mistake and Sutton gets access to a gun and Ballinger finds himself caught in a tense hostage situation.
An armored car is hijacked during a pickup at a government installation. There are surprisingly fews clues left behind by the criminals and Ballinger needs to try and unravel the mystery.
A woman and her baby are hospitalized after a group of bank robbers run them down during an escape. Ballinger wants the men for the robbery but more importantly he wants them to pay for what happened to the woman and her baby
A witness fingers the gangster who cut a rival in half with a shotgun blast, but the killer's alibied by a beautiful actress. The thesp is beloved in ChiTown and has a sterling rep that'll guarantee acquittal. Lt. Ballinger must discredit her story and find out why Tammy's lying for smarmy hood Sandy, who now controls the Loop liquor racket.
Ballinger gets a tip from John Clavell, that an old drug dealer Manny Franchette is coming back into town to re-establish his old network. Clavell wants no part of it having decided to got straight.
Herbie Ryder gains fame for stopping a bank robbery. After a media interview he is shot and killed. Ballinger is brought in in the belief that organized crime has ordered the hit.
Ballinger is brought in when a robbery and murder occurs at an armory. He is puzzled by the list of weapons stolen including a bazooka and other heavy weapons. He knows they cant sell the weapons, so what is their plan?
When an "electronic brain" worth $2,000,000 is stolen and held for ransom of $300,000, Captain Grey and Lieutenant Ballinger devise an elaborate ruse that they hope will lead them to the computer and the thieves.
During a crack down on Chicago crime, Bugsy Page makes threats against the Attorney General Russel Madison. Ballinger needs to decide if the threats are real or simply an attempt to throw the man off.
A badly beaten man is admitted to hospital. He does not have long to live and the police need to work fast to solve the mystery. The man appears unremarkable other than being an identical twin of Ballinger.
A trio of bank robbers try to blow a safe. It all goes wrong and one of the criminals is killed in the explosion. Ballinger thinks there is a connection between other bank vault jobs in the area.
Lanny Cord escapes from a court room and disappears. Ballinger is interested in the case because he's originally arrested Cord and had always sworn to kill Ballinger if he had the opportunity.
British racing car driver Morrison is killed in a local race. The driver's chief mechanic presents evidence to M Squad that indicated the car may have been tampered with before the accident.
Conrad Brenner is found dead in an apparent suicide. As Ballinger continues the investigation it becomes evident that he's actually been murdered, when a personal diary can't be found, Ballinger realizes the truth of the case.
After a narcotics robbery, Ballinger makes an arrest, but is concerned the collar was too easy. Everything about the arrested person does not seem to add up and Ballinger pushes hard for answers.
Frank Ballinger becomes involved in a tense hostage situation, he must restrain his instinct to simply shoot it out because of fears their may be a young child involved.
Ballinger is on a case involving threats against a visiting prince to Chicago. Mo one is taking the situation too seriously until a little girl accidentally finds the detonating device for a home made bomb.
During a robbery one of the criminals is hit in the eye and blinded. Ballinger has a fair idea who is behind the crime. Urgency increases when news comes through an eye specialist has been kidnapped.
Lieutenant Ballinger works to solve a series of armed holdups as a means toward the capture of shotgun-wielding Ma Phelan, who murdered a detective while helping her son Pete escape from police custody.
Ballinger is working a jewelry theft when he becomes convinced one of thieves is a clean skin amateur. He realizes by putting pressure on this individual he has a chance to crack the entire racket open.
A penny arcade owner is robbed and murdered. Suspision falls on a local peddler. But Ballinger thinks there is more to this case than anyone is admitting.
A man is killed while sleeping Ballinger begins to investigate and discovers very different opinions about the dead man's character exist.
Willy Nichols is due to testify in a narcotics investigation, although under police protection he receives a threatening phone call and suddenly disappears. Ballinger must find Nichols to save the case.
Accompanied by a female reporter, Lieutenant Ballinger investigates an elderly woman's charge that the man who robbed her store and killed a police officer was able to escape as a direct result of Officer George Maxwell's cowardice.
Sonny Bradley is charged with murder. Ballinger begins to investigate and quickly realizes something is not right about the statements from the witnesses, and starts see a much bigger game being played.
A plane is blown up killing ten people. Evidence begins to indicate that it wasn't an accident. Ballinger begins to follow the trail and starts to discover a complicated insurance scam in action.
A bookkeeper is robbed and murdered at a circus. A clown named Laslo is identified as the killer. Ballinger and the rest of M squad have to deal with how Laslo could have committed the crime while performing in front of 5000 people in the main tent.
Ballinger and M squad are called in to investigate a diamond robbery. All the evidence points to an inside job. M squad have the tough task of working out who was the inside connection.