It’s an unseasonably warm March evening, and I’m fighting yawns in a stuffy SUV with tinted windows parked on a residential block on the North Side. An hour into my first stakeout, I’m already questioning whether I’m up for the job. Every time someone comes into view, I jump out of my seat: Is that the guy?

“Patience, Grasshopper,” says Adam Campbell, a 64-year-old private eye, when I pester him. Husky and white-haired with a ruddy Irish mug, Campbell specializes in physical surveillance, ideal for nailing cheating spouses, duplicitous employees, and other ne’er-do-wells. It requires persistence, an uncanny ability to blend in, and a superhuman capacity for staying awake in the face of crippling boredom.

“It hasn’t happened often,” Campbell says, “but I have fallen asleep. You work long hours. You get nice and cozy, and suddenly you’re snoring.”

Instead of snoozing, I focus on tonight’s case. A father in his mid-30s has been boozing it up (allegedly), which, according to his soon-to-be ex-wife, makes him unfit to care for their two kids. It’s our job to catch the bastard in the act.

I grew up reading the Hardy Boys mysteries, and I’m a sucker for the cool cars and feathered hair of 1980s detective shows such as Remington Steele. So to learn how a real private eye operates, I decided to spend some time with Campbell, a seemingly hard-boiled type whose LinkedIn page extols credentials like a “generic face” and “keen desire to observe.” He didn’t need a partner. But he got one anyway.

At exactly 7:27, our carousing dad arrives home. All I see is a shadow on the front porch, but Campbell notes every detail of the guy’s attire: dark sports coat, tan slacks, shirt and tie. Campbell grabs his camcorder to time-stamp the moment. Instinctively, I slither down in my seat. Campbell, a former recon specialist with the marines, tells me to chill. “One of the hardest things to do,” he says, “is get over the fact that you know you’re following them but they don’t have a clue.”

The next hour plays out like a scene from Rear Window. I feel skeevy watching this fellow putter around his apartment, but it’s just part of the job for a professional voyeur such as Campbell. He’s been tailing liars and cheats since 1978. He opened his own agency, Heritage Investigations and Surveillance, in 1982 and developed a knack for cases known in the detective biz as “domestics.”

Over the years, for the rate of $85 an hour, he’s followed philanderers on exotic rendezvous, snapped pictures of hooker-happy husbands, and even tracked mistresses whose partners in adultery didn’t trust them. (Takes one to know one, I guess.) After more than 9,500 investigations, Campbell has noticed distinct gender lines. When a woman hires him, chances are she already knows her husband is cheating. She just needs proof to combat lame excuses such as “We’re just friends” or “Honey, that Korean massage parlor is covered by our health insurance.”

Many men, however, can’t even tell him the color of their wives’ eyes. They’re usually blissfully unaware until, say, a buddy tips them off—and then they call Campbell. “My clients don’t need me to get divorced,” he says. “But they need information. They’re looking for me to give them that final push.”

Campbell has witnessed his fair share of couples in compromising positions. I ask if it’s awkward for him to watch other people have sex, and he looks at me like I’m nuts. “Are you kidding?” he says, cracking a smile. “Sex is a stimulating act.” (He appears to view it as a job perk—one that doesn’t happen as much as it used to because, he theorizes, cars are getting smaller.)

Just then, the lights in the apartment go out. “Time to have some fun,” Campbell says, turning on his camcorder. But the dude never comes out. He’s either gone to bed or slipped out the back.

“Sometimes you’re out here and you don’t come up with much of anything,” he explains. “But that’s all my job is: observe and report.” We call it a night.

The next morning, I meet Campbell in the South Loop for another case. This time, the alleged perp is a building manager. His employer suspects he’s abandoning his post to do double duty at another property.

The excitement level is more Matlock than Magnum, P.I. The only difference from last night is that instead of sitting in a stifling car, I get muscle fatigue standing on a street corner. After an hour of praying for something even remotely suspicious to happen, I notice that Campbell hasn’t touched his travel mug.

“It’s a camera,” he tells me. His other little toys include similarly doctored pens and key fobs and the orange traffic cones he puts in alleys to monitor his subjects’ comings and goings. I ask him about the glow under his shirt cuff, assuming it’s some sort of high-tech spy watch. “That’s a Fitbit,” he says.

The hours creep by. Campbell gently scolds me every time I turn around: “Remember, you’re talking to me.” At 1 p.m., I grab a sandwich and miss the day’s only action—the subject’s pulse-pounding two-block walk to Panera.

Near the end of the day, Campbell says he plans to follow the man when he clocks out so he can ID his car for future surveillance. Finally, some excitement. But half an hour goes by and nothing. Did my incessant chitchat inadvertently help the dude elude this veteran PI?

Then I notice a follicly challenged guy in a blue vest and a gray sweatshirt meander across the street. I point him out, and Campbell agrees the description fits. “Let’s go,” he says.

Suddenly it’s like I’m in a scene from a low-octane Bourne movie. The man is about 50 yards ahead, so we quicken our pace. (Out of our way! I imagine yelling as I politely excuse myself for stepping in front of a businessman.) He takes a left and then disappears. Campbell spots him in a bank using an ATM, and we walk through the vestibule, come up right behind him, and confirm … it’s not him.

I’m crushed, but Campbell is undeterred. He’ll be back out here again in a few days. And without his dead-weight partner in the way, he just might get his man.