“If this tunnel goes on for as long as Arvids says it does, a thousand bats could easily have gotten in. Even though cockroaches scatter when attacked, there would be enough insect life down here to sustain them. Silverfish, bugs of that type. Possibly bats from the park moved in here, not migratory ones.”

“Why?” Gentry asked. “It’s still warm.”

“All of the human activity during that rat sweep might have scared them away,” Joyce suggested. “The question is, why would bats have come to this one spot?”

“Would it help if you had samples of guano to study?” Gentry asked.

“No,” Joyce said. “But I do want some pictures. I can scan them into a computer and run some simulations.”

She tucked the flashlight under her arm and pulled a digital camera from her shoulder bag. She snapped photographs from several different heights and angles. Then she put the camera away and shined the light around. Across the tracks to the left was a tunnel.

“What’s that?” she asked.

“It’s a service tunnel,” Arvids said.

“Meaning?”

“The train crews do repairs there, store equipment.”

“Does it lead anywhere?”

“I don’t think so,” Arvids said. “Service tunnels are usually closed. They’re like caves.”

Joyce and Gentry both looked at Arvids.

Arvids grinned boyishly. “I knew it even as I said it. You want to go in there.”

“Bats are at home in tunnels,” Joyce explained, “but they really like caves.”

They swung around a rusty iron column, then ducked low under a concrete overhang. They approached the service tunnel in the pale glow of a single, dusty, sixty-watt lightbulb hanging over the track. They moved ahead slowly. Joyce had informed them that if the bats were there, each next step could bring them into what the animals considered “their territory.” The instant a bat moved toward them, they would retreat.

No bats appeared.

Arvids found the light switch and turned it on.

Joyce stopped nearly halfway into the tunnel and looked around. The far end of the long room was dark. There was a crane to the right, ladders, lockers, and toolboxes to the left. There were also what looked like pneumatic platforms in the ground just outside the tracks. From the oil stains, it looked like railroad cars were probably put on these and raised. She didn’t see guano anywhere. She looked up. The ceiling was about twenty feet high and made of smooth concrete. She was surprised and disappointed.

“Heavy-duty tools, grease stains, and dusty coffee cups,” Arvids said. “No bats.”

Joyce walked ahead while Gentry looked inside the lockers and Arvids checked behind them. Water was dripping down the walls in thin streams. Bats would probably try to follow that to a source; she wondered if there might be another way to get to it.

“Maybe the bats stayed the night in the tunnel outside and then left,” Gentry suggested.

“Like I said before,” Joyce replied. “Not with all that train traffic moving through. No, this is their kind of resting place. Arvids?”

“Ma’am?”

“Are you absolutely sure this is a dead end? No vents, no stairs leading to other levels?”

“I’m positive. There probably are other levels, but they aren’t accessible from this tunnel.”

“When was the last time anyone was in here?”

“I don’t know,” Arvids said. “I could call the stationmaster-”

“Approximately. Hours? Days?”

He looked down at the concrete floor. “The oil stains look pretty dry. I’d say it’s probably been about two or three weeks.”

“No human habitation,” she said. “That would be a definite plus as far as the bats were concerned. So where are they?”

While Arvids and Gentry made their way toward the back of the tunnel, Joyce went to the wall on the left. She walked along, peeking behind the toolboxes and ladders. Then she went to the wall on the right. The crane sat on a platform that resembled the undercarriage of a train car. It rested on a short spur of track connected to the rails in the center of the room.

She squeezed behind the crane. She couldn’t squat there, but she sniffed. There was a smell like ammonia. She smiled. “Bingo!”

“What’ve you got?” Gentry asked as he and Arvids hurried over.

“A bat cave,” she replied.

The men squeezed in behind the crane, and Arvids pointed the flashlight down. There was an oval hole just above the base of the concrete wall. It resembled the hole in the main tunnel except that it was close to the ground and was only about two feet tall by two feet wide.

“It’s another entrance for the tunnel people,” Arvids said.

“Yes,” Joyce said, “but smell.”

“More guano,” Gentry said.

Joyce reached up. “Arvids, can I have the flashlight?”

Arvids went to hand it to her. Gentry stopped him.

“What are you planning to do?” Gentry asked.

“Go inside.”

“That’s what I thought. I can’t let you do that.”

“What are you talking about? I have to see if the bats are still here. If they are, we’ll have to come back with bat suits, get specimens. See if there’s something wrong with them.”

“I’ll go in,” Gentry said. “You’re going back to the station.”

“No way!”

“Did you take a close look at the wall?” He pointed to the corner.

She looked back down. “I don’t see anything.”

“The lower left corner. See that jagged piece like anM?”

Arvids turned his flashlight in that direction. Joyce looked closer. There was blood on the sharp edges.

“That could be from anything,” Joyce said. “A homeless person could have cut himself when he went in. Or it could be blood from a wounded rat or bat. Anything.”

“You’re right. But until we know for sure, I want you out of here.”

“Robert, that’s crazy! This is a scientific puzzle. Let me do my job!”

“You did the job you came out here for,” Gentry replied. “You saw the guano on the tracks. You took pictures. That’s enough.”

“No! My job isn’t finished until we’vefound the bats. Can you feel the air coming from behind the wall?”

“Yes.”

“It’s warm and damp. This is where the bats have gone. Ihave to go in and look around.”

“Maybe later,” Gentry said. “After I’ve checked it out.”

“This is insane! I’ve picked my way through quicksand fields, I’ve explored caves with just matches-”

“That was the wild. This is New York.”

“Oh, please!”

“Listen to me,” Gentry said. “Those tunnel people Arvids was talking about can be extremely territorial. I used to bump into them when I was down here. There might also be structural deficiencies behind the wall that we don’t know about.”

“The detective is right about those things,” Arvids said.

“I’ll take my chances,” Joyce replied.

“I’m sorry,” Gentry said, “but that’s not an option.”

“I don’t believe this-”

“It’s nothing personal,” Gentry said.

“No, it’s insulting!”

Gentry excused himself. He went over to one of the lockers and got a flashlight. He tested it, then walked back to Arvids. “Let me have the radio.”

Arvids handed it to Gentry.

Joyce’s lips were pressed tightly together. “And what exactly are you going to do inside?”

“Look for bats.”

“Look for bats. And how are you going to read what you see? Genera, guano color, maternity roosts-”

“I’ll make very careful observations and report back. That’smy job.”

“It won’t be enough,” she said. “You won’t be able to tell an invasive species from an indigenous one, a sick bat from a healthy one. You need someone who knows what to look for.”

“You can come back later-”

“If you do find bats and they’re anything like the Westchester bats, there may not be a later.”

“In that case, your being there won’t help.”

“I disagree. I’ve had to improvise in the field.”

“Me too. Look, I understand and I’m sorry.” Gentry glanced at Arvids and cocked his head toward the main tunnel.