At the beginning of the first episode of M Squad, the hardboiled cop show filmed here from 1957 to 1960, we see the marquee of the Chicago Theater, lit up in glorious, gloomy black and white. Then we hear the deep, whiskey-and-Pall Mall-cured voice of Lee Marvin, who starred as Lt. Frank Ballinger, letting us know where he’s from, who he is, and what kind of business he means.

“Chicago, that’s my town; it’s no different than any other city, large or small. It’s the second most populated area in the land, and the hub of our country, so our police department’s kept busy. M Squad is a special section of the Chicago Police Department whose members can be assigned to any and all divisions, from fraud to homicide.”

Marvin steps out of his massive Ford sedan, with the Michigan Avenue bridge and the Wrigley Building in the background, and introduces himself.

“My name’s Frank Ballinger, detective lieutenant. I love Chicago. Why? Like I said, it’s my town. I like its people. I like helping them. I guess that’s why I like being on M Squad.”

M Squad was one of the first TV productions set in Chicago, and because of its unflinching look at our city’s crime and corruption, it was the last, for a very long time. The show’s significance in television history reaches far beyond our borders, though. M Squad was the quintessential noir drama, and the greatest distillation of ’50s cool ever committed to a small screen.

The show’s style began with its star. Marvin’s lanky frame and menacing face made him look badder than any of the bad guys he chased around town in that black Ford. He wore a gray suit, a skinny black tie and a fedora— the uniform of the Serious ’50s Guy—with far more panache than Don Draper would decades later. Like his successors Joe Friday, Steve McGarrett and Lennie Briscoe, Ballinger was all cop, all the time, a loner with no life outside the law. By his own admission, he was “a bachelor living in a furnished flat,” and only employed his masculine wiles to seduce dames who might give him the straight dope on some hinky deal he was investigating. Marvin was often cast as a villain, but in M Squad, he was on the side of truth, justice and The Chicago Way.

M Squad’s plots were torn from the pages of the pulp detective novels that filled drugstore carousels in those days. Some were inspired by Chicago police Capt. Frank Pape, head of the robbery division, whose exploits filled the pages of True Detective magazine. Ballinger arrested an endless lineup of bookies, con men, shake-down artists, mugs, thugs, fixers, pushers, pimps, safe crackers, and gun-crazy bikers out for kicks and cash. He did it all to a moody jazz score, and in the same long-disappeared Chicago Nelson Algren chronicled in The Neon Wilderness. M Squad recorded plenty of brightly lit come-ons for liquor, cigarettes and dancing, and lots of signs for Meister Brau, which was brewed on North Avenue until 1965. (Also lots of shots of the Wrigley Building, then the city’s most picturesque skyscraper.)

In one episode, Ballinger posed as a Hungarian laborer to break up a protection racket preying on immigrants. “Nobody’s gonna have to pay extra for living in Chicago if I can help it,” he declared. In another, he sought out a stoolie named Johnny Roscoe in a pool hall, to find out whether a dirty cop had been offering protection to gamblers.

There was no dirty cop that night, but on January 30, 1959, M Squad aired “The Jumper,” an episode about a cop who kills one of his colleagues to prevent him from squealing about corruption in the department. Mayor Richard J. Daley was so outraged by the intimation that his cops were corrupt that he more or less banned movies and TV from his city for the next 20 years—starting with M Squad.

“We shoot locations, twice a year,” Marvin would say. “No permit, no cooperation, no nothing. They don’t want any part of us. Any public building, but nothing else, no stopping traffic. We shoot it and blow.”

(Marvin was often shown walking toward M Squad headquarters, actually a closed-down police station at Racine and Superior, since demolished to make way for the Kennedy Expressway. You can also see him standing next to the Nathan Hale statue in front of the Tribune Tower.)

With few exceptions, that ban lasted until Mayor Jane Byrne welcomed The Blues Brothers to town.

M Squad does have a more lighthearted legacy, though. It was the direct inspiration for the short-lived TV series Police Squad!, and the much more successful Naked Gun movies. Police Squad!’s pilot was a shot-for-shot parody of M Squad’s “More Deadly,” about a double murder at a currency exchange, committed by a clerk who’d been embezzling to pay her bookie. Its big band theme song was a knock off of the Count Basie composition that introduced M Squad. And, obviously, Leslie Nielsen’s deadpan Frank Drebin was inspired by Marvin’s no-nonsense Frank Ballinger. (Watch a side-by-side comparison here.)

For all that, M Squad is probably the greatest cop show—and the greatest Chicago show—you’ve never seen. MeTV aired episodes a decade ago, but M Squad is not available for streaming anywhere. The show may not suit 2020s sensibilities. Ballinger never worried about accusations of police brutality, pasting one onto the mug of a homicidal sailor he tracked down on a ship about to sail for Toronto, and gunning down any stiff who even reached for a sidearm. (In “Dead or Alive,” a young reporter from a North Side newspaper criticizes Ballinger for declaring he wants a suspect “dead or alive”; the detective ends up rescuing the little bleeding heart from the criminals she’s been trying to protect.) It is on DVD, though, and the Chicago Public Library has a few copies, plus an LP of music from the show. Watch it, for a look at a Chicago you’ve never seen before—and will never see again.