LAST WINTER I WAS COACHING youth hockey with a guy named Mark Donahue, who said he had a great idea for my next book. Upon hearing that phrase, I almost always change the subject, but Donahue is not the sort of person who usually suggests literary topics to me. With his square Irish face, jug ears and modified high-and-tight haircut, Mark Donahue's appearance belies his roots in the tenement district of Somerville, Mass., a hardscrabble town right outside of Boston. He's kind to children, solicitous to his wife, and cheerful enough with the other hockey coaches, but he's not a bookish fellow and has a real city kid's edge to the way he goes about things. Donahue and I both live in Methuen, a quiet place about twenty-five miles north of the city, on the New Hampshire border. (I often kid Donahue that, like everyone who grew up surrounded by pavement, a lot of Somerville guys moved here when they saw their first pine tree, thinking they had reached the White Mountains.)

In Methuen, the local grocery store puts out three copies of The New York Times every morning, and two of them are still there, unsold, when the store closes at nine o'clock. It's pretty much a blue-collar town, and most of the people I know are too busy roofing, paving, installing boilers, growing apples, or fighting fires to even consider what I might be interested in writing about. Even after I've published two books and seen my work appear in newspapers and magazines across the country, the first question I hear whenever I see someone I know is “You still writing?” like it's an affliction that I'm bound to get over. And if I'm ever approached with any enthusiasm, it usually means someone wants me to write about his impending divorce, or a piece for The Eagle-Tribune on his snow-plowing business.

So when Mark Donahue told me that he was a cop and a private detective, and that his mentor, the recently deceased Joe McCain, Sr., put all fictional detectives to shame, I became intrigued by the notion of working for McCain Investigations and writing such a book. Like all the kids in my neighborhood I grew up on detective stories, and when I was quite young thought that the English actor Basil Rathbone was Sherlock Holmes and that old black-and-white films like The Hound of the Baskervilles appearing on the Saturday matinee were some kind of primitive home movie. Sometimes I even crawled around with a magnifying glass, wearing two baseball caps back to front as I searched for clues to God-knows-what in the dusty reaches of my basement.

My favorite television show was The Rockford Files, and its star, James Garner, who lived in a beat-up house trailer in Malibu and kept his revolver in a cookie jar, was my idea of the ultimate detective. Forget Ironside and Cannon and Mannix, I was a dyed in the wool Rockford guy. Whether zooming up the coast in his gold Firebird or hurting his knuckles after punching a wiseguy, ex-con Jim Rockford was Everyman in a checked sport coat, a guy who, like me, enjoyed eating tacos and drinking beer and kept his accounts on the back of a wrinkled envelope. For nearly five years I was occupied on Friday nights, lost in the gritty details of Jim Rockford's caseload, and therefore predisposed when Mark Donahue uttered the words “private” and “detective” in the same sentence.

What Donahue was offering was a chance to go beyond the realm of television detectives, where the moral boundaries are black and white and even the most convoluted cases are wrapped up in under an hour. Roughly the same age, size, and complexion as Jim Rockford, Mark Donahue is an affable, gregarious man who dotes on his seven-year-old twin son and daughter. But on the street, he can change mien very quickly when challenged or threatened: his eyebrow arches up, his face darkens, and his voice drops into a guttural throb. Big Joe McCain and his operatives were all trained at the School of Hard Knocks, and almost all of the dudes opposite them— the junkies, bank frauds, and rogue cops— were a lot more experienced at the game than I was. At McCain Investigations, I'd be sent looking for people who didn't want to be found, following guys who didn't want to be followed, and entering neighborhoods in Somerville and Roxbury and Hyde Park where I was not at all welcome. It would be entertaining, no doubt, but there would be no commercials, no time-outs, and no “do-overs” if somebody got shot or stabbed or run over. These guys were playing for keeps.

Headquartered at 106 Fulton Street in Boston's North End, McCain Investigations has been in business for the past fifteen years, tackling everything from wife beatings and warehouse rip-offs to international smuggling and gangland murders. Staffed by tenacious, hard-nosed detectives with years of experience, the company specializes in covert video camera, environmental, and “general” investigations. Cases last from a few days to several months, and their client list includes jilted spouses, nervous business executives, endangered celebrities, wary corporations, and suspicious attorneys.

One area in which McCain Investigations has excelled is the recruitment and training of new investigators. Good thing, since other than an eye for detail, a good ear, and the ability, inherited from my late mother, to size people up upon meeting them, I have zero experience as a detective. Mark Donahue noted that it takes a solid year to break in a new investigator, as it takes that long to encounter the various types of cases. That was all the time any of us had.

Joe McCain, Jr., president of the company and its founder's namesake, is a police sergeant in Somerville, drummer in local bands, motorcycle enthusiast, and father to three rambunctious young sons. McCain's childhood pal Mark Donahue has recently been appointed to the police department in Salem, New Hampshire, has a young family of his own, and is working the graveyard shift in a cruiser. And Detective Kevin McKenna, a Boston Housing cop, has started working part-time for a P.I. firm closer to his home. In the months since big Joe's death, the three men have tackled enough cases to keep the doors open at McCain Investigations but have reached the sad conclusion that the business should be dissolved. At the end of the year, McCain Investigations is going to be sold to a guy interested in big Joe's client list and office space. By joining Mark and Joey and crazy Kevin McKenna for their last run, I'd have a once-in-a-lifetime opportunity to walk in the footsteps of Joe McCain, Sr., one of the most decorated cops in Boston history, and to steep myself in the history of a company and a profession whose core values are straight out of the Old School.

BENEATH THE LEGEND “WE NEVER SLEEP” and the world-famous logo of the unblinking eye, the former Scottish barrel maker Allan Pinkerton opened his Chicago private investigations firm in 1850. The Pinkerton National Detective Agency was the first of its kind in the United States, and Pinkerton and his sons, William and Robert, were involved in some of the most notorious cases of that century: the pursuit of Jesse and Frank James and shooting of the Younger brothers; the disruption of the “Wild Bunch,” including George “Butch Cassidy” Parker and Harry “Sundance Kid” Longbaugh; the conviction and hanging of the Missouri Kid; and a foiled assassination attempt on Abraham Lincoln aboard a train to Baltimore in 1861.

In 1875 the undercover Pinkerton man James McFarland infiltrated a secret terrorist organization known as the “Molly Maguires,” resulting in the execution of nearly two dozen of its members. And early in the 1900s, an ambitious young man from St. Mary's County, Maryland, named Samuel Dashiell Hammett worked a series of cases as a Pinkerton operative. His experiences formed the backbone of his indelible character Sam Spade and filled in the plots of The Maltese Falcon and The Glass Key, literary detective novels that are still being read the world over.

Even more than its most celebrated cases, however, the legacy of the Pinkerton Agency lies in the structure and intelligence of its investigative methods. Its Chicago headquarters became the original database of criminal activity, where meticulous files were kept on an ever-growing collection of wanted men and women, each of them adorned with another Pinkerton innovation— the “mug shot.” And although Pinkerton himself was reported to have an outsize ego and botched some high-profile assignments, he was known as dogged, indefatigable, and incorruptible.

Despite all their state-of-the-art equipment and access to global information, the detectives at McCain Investigations are not that far removed from the golden age of sleuthing. Big, bluff Joe McCain, Sr., was, like Allan Pinkerton, a determined fellow who could handle himself and handle a gun, yet understood that his brain was a more potent weapon than his fists or what he wore on his hip. Both men knew their way around a courtoom and a barroom, and their daily lives brought them in contact with some of the most dangerous and influential figures of their time. When confronted with the facts of Joe McCain's life, few would disagree that he was what used to be referred to as “the genuine article.” In a city where, for some inexplicable reason, chefs and restaurant owners are considered celebrities, and in a society that often confuses victims with heroes, Joe McCain is as close to the Greek ideal of the hero as an Irish kid from Somerville is ever going to get. His highlights are exemplary: taking a bullet while gunning down a homicidal drug dealer; going toe-to-toe with the ferocious mob hit man Joe “the Animal” Barboza; unraveling sophisticated criminal activities leading to hundreds of high-profile arrests and convictions; the list goes on.

But the true measure of Joe McCain's character lies not in the arrests he made or the lives he saved, but in the quiet moments he reveled in. How he loved his wife and son and friends and was more at home walking his dogs on Packard Avenue than at the testimonial dinners that marked his career. How for twenty-four years he dressed in a red suit and snowy beard— augmented by his own white hair— and as Santa Claus spent the entirety of Christmas Eve visiting his friends' and colleagues' and their neighbors' children, and homeless kids and kids with AIDS, sometimes arriving via State Police helicopter to meet all his appointments in one night; ending at home with his three beloved grandchildren, who lived upstairs and worshiped him. How he counseled the wildest lads from the old neighborhood and beyond, like Leo Martini, whose brother was a Met cop turned bad that ended up in jail and who became a cop himself and leaned on big Joe when the other side beckoned. And Timmy Doherty, who crossed the blue line and testified against a dirty cop, and guys like Brian O'Donovan, hailed as the “toughest guy in Somerville.”

Not to mention the men and women big Joe put in jail and later befriended, and the victims of crimes he continued to advise and comfort and counsel long after he'd sent their tormentors to prison, and crooks turned informants he treated with genuine respect and meted out rewards and admonishments to with the forbearance of a kindly Dutch uncle. Joe McCain did all that, and still found time to assemble a pretty good golf game for a man over three hundred pounds with a couple of bullet holes in his stomach.

Although he was larger than life, in no single photograph does Joe McCain stand more than five inches tall. And I know him only via photographs, audiotapes, fleeting bits of old television interviews, and yellowed newspaper clippings; and through the tales and anecdotes of his former colleagues, neighbors, and friends. Certainly it would be easy to look at McCain's accomplishments and chalk them up to his Depression-era roots or membership in the “Greatest Generation.” But it's a peculiarity of heroism, especially in the classical sense, that the hero strikes out alone— that he has the inner strength and absolute conviction in his own ideals and abilities to go against the grain of his fellow stalwarts. In an era when “reality” has become something we watch on television, the great pageant of Joe McCain's life is well worth examining. A genuine hero doesn't endure a single moment and then traffic in it. He or she doesn't take as the main goal parlaying the heroic experience into something else. As Winston Churchill demonstrated in World War II, being a hero is much less glamorous and more difficult than that. Simply put, a hero lives the truth.

It's difficult to tell a story about being a detective that isn't episodic and profane because that's the nature of the work; if you want politeness, continuity, and closure, go sell real estate. And certainly among cops in Boston and everywhere else, there's a fair amount of small-mindedness and bullying, and more than a few guys whose uniforms cover up their dearth of personality, but you only have to spend a night in a place like Somerville or Fall River or Lawrence to imagine what it would be like without them. So when a detective like Joe McCain, Sr., comes along, with his hard-knocks childhood and wartime naval service, with the street contacts and smarts, who can drink like a sailor and punch like a kangaroo and has the balls of an elephant, a guy who really enjoys the game and plays hard, you wind up with a collection of feats that, had they occurred in another age, would've been the sort of life the bards wrote songs about back in the old country, in Cork.

In Legends of Winter Hill, I'll serve the twin roles of “newsie” and gumshoe, creeping down alleys, interviewing witnesses, poring over files, and in the end, creating a portrait of a career and a calling that has intrigued us since the days of the original Pinkerton men.