“Well, most folks don’t realize it, but the reason the subway tunnels are different sizes and connect at certain stops but not others is because, prior to the MTA, the subway was run by three companies—all with their own plans and schematics. That’s to say, this F train is the IND and it can’t run on the original IRT lines because they’re too narrow. So the MTA has all these workarounds. In fact, my pop told me stories about starting his patrol in one neighborhood and coming out in a completely different precinct, just by walking underground. MTA didn’t even have complete schematics of their own system in the ’80s—that’s why they’ve got half-finished tracks, tunnels that lead nowhere, abandoned lines discovered during construction…. I wouldn’t be at all surprised if they still didn’t know about some of what’s down here. That’s what makes it a haven for the mole people.”

“Mole people,” Larkin repeated.

“You’re not supposed to call ’em that,” Armstrong replied. “But some embrace the term.”

“Why do you know this,” Larkin asked.

Armstrong laughed cheerfully and said, “I’m a bit of a train geek. Me and my dad have been going to conventions every year since I was waist-high. We love it. Everyone’s got a thing, you know?”

“I suppose so.”

“Anyway,” he continued, “The Q was suspended in the late ’90s for track repairs, and Fifty-Seventh was the final stop. It was a convenient station to hop the tracks and head uptown to the BMT line at Sixty-Third. That was used to store non–rush-hour trains until the Second Avenue Q line finally opened a few years ago.” Armstrong stopped walking, turned, and cast his flashlight on Larkin and Doyle. “All it’d take is one person trying to keep off the grid to discover the relative seclusion of those tracks, and bam, encampment.”

Armstrong began walking again, the scuff and crunch of his boots echoing off the arched walls and rounded ceiling.

“That wouldn’t be the case anymore, though,” Doyle called. “Right? Because of the new Q line?”

“Lots of nooks and crannies to hide in, Detective. Pop once found an access point some kids were using. They called it ‘The Hole,’ and that’s exactly what it was.”

The air was growing more humid and stagnant the deeper they walked, and perspiration prickled under Larkin’s arms, beads of sweat following the curve of his spine. He noted that the accumulated garbage, due to either obnoxious riders purposefully tossing it onto the tracks or the rush of wind that followed trains entering and exiting stations picking up loose debris, was thinning considerably, making the refuse that was present stand out in a more blatant manner.