"Somebody tell me again why we're down here?" Mikey asked, eyeing the crumbling walls of the underground tunnel.
"Donny thought he picked up some kind of scratching sound on his security equipment. We gotta check it out so that we know somebody ain't tryin' ta find the lair," Raph explained.
"Oh, okay," Mikey said. "You know, life would be a lot simpler if Don would get a hobby. Maybe he should take up stamp collecting or litter art."
Raph snorted. "Litter art? From the looks of your room, I'd say that hobby was already taken."
"Shush you two," Leo told them. "Don is trying to pick up that sound again."
Don shot them a look, his earphones on, a small microphone in one hand and an audio analyzer in the other.
Silence fell around them and Mikey nervously shifted from foot to foot. His brothers were in front of him, moving slowly as Don swept the microphone around the tunnel. Mikey enjoyed movies about monsters in underground caverns way more than actually hunting for unexplained things in underground caverns.
A movement caught his eye and he snapped his head around in time to see something shiny and green slither past the opening into the intersecting tunnel.
"Eeep!" he screeched and jumped towards his brothers.
"What the shell?" Raph yelled as Mikey slammed into him.
"I saw something!" Mikey shouted, pawing at Raph's shoulder. "It was big and slimy and ugly and green. And this time it wasn't Raph," he added.
Raph punched him in the back of the head. Don and Leo ran past them, going in the direction that Mikey's waving hand had indicated. They reached the tunnel junction a couple of seconds before their bright banded brothers did.
"Which way was it going, Mikey?" Leo asked, his head twisting from left to right.
"That way." Mikey pointed to the right.
Don held his microphone out towards the seemingly empty tunnel. The digital bars on his analyzer registered nothing at first, but when he took a few steps forward, the bars jumped almost imperceptibly.
"I'm picking up a very faint sound coming from down there," Don told Leo, who was standing next to him.
"It's probably rats," Raph said. "Mikey saw one and his imagination turned it into the slime people from Mars."
"Guys," Mikey called in a low voice, "don't you recognize that tunnel? It's the one that leads to the opening in the wall that Sydney made. The one that takes us down into the old subway line."
Don shot a glance at Leo. "You don't think there are any more of those poor mutated creatures from Shredders experiments still roaming around down there, do you? Sydney said that everyone was in the underground city with her."
"He could easily have been experimenting with another group of people that she never knew about. We need to find out for sure," Leo said as he led the way into the tunnel.
Mikey shook his head and grimaced. "Oh man, I knew you were gonna say that."
Raph grabbed the edge of his little brother's carapace and yanked him in the direction that Leo and Don were going. Leo reached into Don's bag and extracted three flashlights, holding onto one and passing the others to Raph and Mikey.
Mikey's eyes were darting from left to right as he trailed along behind his brothers. He kept one hand on his nunchucks, ready to pull them at the slightest hint of trouble.
Don's eyes were focused on his analyzer. He could still hear the sibilant noises through his earphones. Leo walked next to him, glancing periodically at his brother before turning to watch the tunnel ahead of them.
Raph was a couple of feet back of Leo's right shoulder, his attention directed towards the walls. He remembered that the Shredder's mutated test subjects had the ability to move through stone. Raph wasn't in the mood to have some creature suddenly smash through the rock wall and attack them.
He was the first to see something glistening on the ground near the base of the tunnel wall. Raph turned and walked towards it, noticing that there was a long line of some shiny substance trailing along the ground.
When he pointed the flashlight directly at it though, it disappeared. He tipped the light upwards and could see the greenish color shimmer once more.
"Guys," Raph called to his brothers without taking his eyes off of the substance.
The others stopped and turned back to look at what had drawn Raph's attention.
His brothers trudged through the ankle deep water to join Raph as he kneeled in front of his find. Their flashlights were turned in his direction and he waved a hand towards them.
"Turn off the light," Raph said, flicking the switch on his.
The other two flashlights were extinguished and the greenish glow became immediately visible.
"Whoa," Don said in a breathy exhale.
Kneeling next to his brother, Don handed his microphone and audio analyzer up to Leo. He leaned further over as he studied the glow and one hand moved towards the substance.
Raph's hand shot out to grab Donatello's wrist. "No touchy, science boy. Ya' don't know what that is."
Don nodded absentmindedly and without taking his eyes off of the glow, reached into his duffel bag. Digging around inside of it for a moment, he finally extracted a small sample jar. Uncapping it, he carefully scooped a good sized amount of the glowing earth into the jar.
Tapping the jar against the tunnel wall to dislodge the earth clinging to the outer lip, he screwed the cap on tightly and held the specimen up to his eyes.
"Fascinating," Don murmured, running the tip of one finger across his chin. "Is it a chemical of some sort that's causing it to luminesce? And how did it get down here in the sewers?"
"I'll tell you how it got down here," Mikey answered in a frightened voice, "it came off the monster I saw slithering down this tunnel."
"Can it Mikey," Raph growled as he stood up.
Don placed the sample jar in his duffel and rose to his feet as well. "We should follow this trail. I made a batch of the crystal serum and brought a couple of syringes with me just in case the sound we heard belonged to another mutated human."
"Just in case, Donny?" Leo asked with a smile.
Don shrugged, "I like to be prepared."
"Following that trail means we walk in the dark," Raph pointed out.
"Dark?" Mikey's voice was querulous. "Um, maybe one of use should go back to the lair and let sensei know what's going on. I volunteer."
Raph stepped behind his kid brother and gave him a shove. "Move along chicken little."
Mikey reluctantly followed Don and Leo, with the occasional prod from Raph when his feet wanted to stop. It wasn't that he didn't want to help some poor soul who might have been mutated by the Shredder, he just didn't want to rush into it quite so fast.
Don was still studying his analyzer as they walked, with Leo reaching out to periodically guide him so he wouldn't slam into a wall. Don could sometimes focus a little too well.
By Mikey's best estimation, they were drawing near to the hole in the tunnel wall that led down into the old abandoned subway tunnel.
Just as Mikey feared, the shining green trail they were following led them straight to the hole. Not only that, it ran up the wall and into the opening.
Mikey stared at it for a moment and then said, "You know, somehow I could have guessed it would go in there."
Don pushed the hand holding his microphone as far into the hole as he could. The bars on the analyzer began to jump, and he turned to where Leo stood close by him, nodding an affirmative.
"We're going in there, aren't we?" Mikey asked in a resigned kind of way.
Leo answered without looking at him. "Yep."
"May I just point out that the last time we followed something into that rabbit hole we had a lot more of our gear with us?" Mikey told him.
This time Leo did glance back at his youngest brother. "I know Mikey. We won't go far, just to the point where the train sits. I'd like to have some idea of what we might be facing."
"Most of the area caved in the last time we were there. Don't know that the rest of it is all that stable either," Raph said.
"Then we shouldn't make a lot of noise," Leo replied, climbing into the tunnel first.
Don followed him and Raph flicked on his flashlight, aiming it at Mikey's face.
"You next, Mikey," Raph said.
"Oh, I don't mind bringing up the rear," Mikey answered with a nervous grin. "It's a tough job, but somebody has to do it."
"Yeah, that somebody is gonna be me," Raph said. "Move it."
Mikey muttered under his breath and unenthusiastically stepped into the opening in the wall. Once he was inside, Raph followed.
Leo used his flashlight while they were inside the passage. The first time they had gone this way, there had been no other openings to investigate and that hadn't changed. Once or twice he turned the light off so they could verify the green glow was still there and then they continued on.
As they neared the end of the passageway, Don hissed a warning to Leo, who quickly extinguished his light.
"What is it Donny?" Leo asked, his voice low.
"The audio detector picked up a spike in sound just now," Don whispered. "It's dropped down to almost nothing at the moment. Maybe something or someone heard us coming."
Mikey pushed in close to his brothers. "Of course it heard us. Don't you know monsters have great hearing? It's probably just on the other side of the opening waiting to eat whoever walks through there first."
"I volunteer Mikey," Raph whispered. "It's a tough job but . . . ."
He didn't get to finish the sentence as Mikey elbowed him in the stomach.
"Enough you two," Leo said in a hushed tone. Quietly withdrawing a katana, Leo told them, "I'm going first."
Raph pulled a sai from his belt and glided up next to his big brother. "Not without me ya' ain't."
Leo glanced at him, a corner of his mouth quirked up into a smile. Side by side, the two warriors stepped out of the passage and into the subway tunnel.
Nothing was waiting for them. In fact, everything appeared to be the same as the first time they had come this way, except for the collapsed section of tunnel to the right.
Don and Mikey stepped out a moment later. Don turned his analyzer and microphone towards the section of tunnel that had fallen in and registered absolutely nothing. When he pointed it in the opposite direction, the bars on the meter jumped.
"This way guys," Don pointed to their left.
Flashlights off, they could see a faint trail of the glowing green substance they'd been following. It wasn't as heavy as before; some places were mere splotches of color.
"You know, undersea life forms uses luminescence as a survival tool," Don said. "The light draws in prey so they can eat."
"Really didn't need to know that Donatello," Mikey said in a not too pleased tone of voice.
"Sorry Mikey," Don replied, slightly chagrined.
"If something is up there waiting ta eat us, it's gonna be real disappointed by the steel I'm gonna feed it," Raph said, his voice low.
After a few more yards, the green glow jogged across their track and into one of the abandoned subway cars. Leo turned his flashlight on and peered inside the open doorway.
"I don't see anything," he told them over his shoulder. "The dust doesn't even look as though it's been disturbed." Turning off the light, he remained in place for another moment before withdrawing his head. "I can see splashes of the green shimmer in here though."
"Maybe that's its blood," Mikey said, his eyes wide. "Maybe something got wounded and is trying to get home."
Raph grinned mischievously. "Yeah Mikey. Maybe it's one of those Predators like from that movie. It's probably invisible and sitting on top of one of these cars waiting to hunt you down."
Mikey shot him a mean look. "That's not funny, Raph."
"Could you two please keep it down?" Don asked mildly as he tried to scan for further sounds.
The bars on his analyzer were barely moving, but they did seem to indicate sounds coming from further along the tunnel.
"Let's keep moving," Leo said, following the rail line.
They had only gone a little further when they heard a crunching sound. All four of them automatically looked towards the ceiling and support beams.
The walls were smoother in this section of tunnel; the wooden supports doubled in most spots. There were no cracks in the walls; none in the support beams.
Don shook his head as Leo played his light from one side of the ceiling to the other.
"This must have been a service junction," he said. "Notice the redundancy in the supports? I don't know what that sound was, but this area doesn't look like it's ready to fall in like the other section did."
Mikey leaned towards Raph and murmured, "That's one of those good news, bad news statements. The good news is we don't get crushed; the bad news is we have to keep looking for monsters."
"Ya' know, we didn't just imagine that sound," Raph said, ignoring Mikey.
Don was studying his analyzer as Raph walked past him. "I realize that. It must have been something else."
"Oh, something that sounds exactly like wood breaking in half?" Raph said sarcastically as he moved further into the tunnel.
As he passed under a section of the double wooden supports, they heard a loud snapping noise. Freezing in place, Raph looked back at Don for an answer as to where it was coming from.
Mikey looked up and saw one of the beams move. Diving forward as quickly as he could, he caught Raph around the waist and threw them both to the ground as the heavy wooden timber crashed down exactly where Raph had been standing.
Dust flew up in the small space and had them all coughing. Leo and Don rushed over to where their brothers lay, pulling them to their feet in case the rest of the roof started to cave in.
"Shell!" Raph exclaimed, seeing the beam that had almost crushed him.
"Are you guys okay?" Don asked, eyeing the ceiling suspiciously.
"Peachy," Raph said. Reaching over, he gave Mikey's shell a rough pat. "Thanks bro'."
Mikey grinned at him, then turned to Don. "How did that happen? I thought you said this section was secure."
Don walked over to the wall and examined the standing support beam that had previously held the fallen timber.
"Leo, can you shine your flashlight up here?" he asked.
As the light hit the top of the post, Don's face grew grim.
Pointing at it, he turned to his brothers and said, "That's been cut through and it's fresh."
"Fresh?" Mikey asked. "As in, just now fresh?"
"Yes and very fresh," Don answered both questions as Leo stepped over to look for himself.
"Those aren't the marks of a blade Donny," Leo told him.
"Maybe a chisel?" Don guessed, examining them further.
"How the shell did something stand there and chisel that board loose with the four of us standing right here?" Raph asked, his hands on his hips and his gold eyes flashing.
"Dude," Mikey said with a huge exhalation of air, "maybe it is invisible."
"Mister invisible is still leaving a trail," Raph pointed to the ground.
Apparently whatever they were following had gone into a subway car and back out again, because the green glow was shining a thin trail along the dirt.
Leo hesitated. "Maybe we should go back to the lair and get some supplies before we go any further."
"Uh, uh," Raph said. "I'm good and mad now. Whatever just tried ta brain me is leaving bread crumbs ta its destination and I owe it a beat down."
He was moving before Leo could disagree with him.
"Hot head," Leo muttered under his voice and followed.
"Predictable," Don murmured as he turned to catch them.
"Oh man," Mikey moaned, breaking into a run so he wouldn't be left behind.
Raph's flashlight picked up another group of subway cars just ahead of them. The rail followed an upwards slope of ground that flattened out under the cars. Raph was striding up that incline with a grim purpose when Leo caught up to him.
"Slow down, Raph," Leo warned. "If there's another trap you're going to walk right into it."
Rather than argue with Leo, Raph slowed enough so that Don could join them. His microphone was held out at arm's length and his eyes were glued to the screen on his analyzer.
"I'm still getting the same band width reading," he told them. "In fact, it's a bit stronger now."
"So maybe whatever we're chasing has decided ta wait for us," Raph said. "Good."
While his three older brothers stood talking, Mikey started to become aware of a change in the atmosphere. He looked around at the walls and then down. Mikey thought he felt the ground moving against the soles of his feet and then he saw the dirt begin to jump.
A heavy rumbling sound drew everyone's attention and Mikey was pretty sure he knew what it was.
"Get off the tracks!" he yelled at his brothers.
One of the subway cars was rolling towards them, gaining speed on the slope. Leo and Don dove to the right of it; Raph jumped left.
The car swept past them and a second later crashed with a resounding crunch of metal on metal as it hit one of the parked cars they'd already passed.
"Bet that wasn't an accident either," Mikey said as he ran up to his brothers.
The other three stood up and brushed the dirt off themselves. Don retrieved his microphone from where it had fallen, but the analyzer had dropped onto the tracks and was smashed to pieces.
"My analyzer," Donny moaned, squatting next to the remains. "Do you know how hard it was to get one of these?"
"Never mind that, genius," Raph said. "We don't need it. We still got that shiny trail we can follow."
Don stood up and removed his earphones, tucking them and the microphone into his duffel. He hesitated a moment with his hand in the bag and then brought out the jar he'd collected the glowing sample into earlier.
"It stopped glowing," Don said, holding it up for his brothers to see.
Leo reached out and took the jar from him, turning it around as he examined it.
"The shine wears out?" he asked.
"Bioluminescence," Don said with something like awe.
He retrieved the jar from Leo and held it up in front of his eyes, shaking it a little. A tiny flash of green lit the interior and then faded.
"Bio whatsis?" Mikey asked.
"Bioluminescence is light produced and emitted by a living organism," Don answered. "Cold light. That green glow is alive, or at least it is for a little while."
"So what we're following is leaving a trail that's alive?" Raph asked. "What kind of sense does that make?"
"Maybe that's its dinner," Mikey offered. "Maybe it'll see our flashlights and think we're its next meal."
Raph growled at him as Leo quickly said, "Whatever else it means, it also tells us we need to move or we won't have a trail to follow."
Don quickly put the jar away, pulling out a flashlight of his own. Shining their lights up the track, the group determined that the rest of the subway cars appeared to be stable. Turning the lights off, the glow of the trail they followed was visible alongside the tracks.
The Turtles walked in silence, moving as fast as they dared. The green shimmer seemed to be getting fainter, sometimes disappearing completely before one of them found a glowing segment.
It was several minutes before any of them realized they were hearing a dripping sound. They had passed a couple of dilapidated subway cars, noticing that instead of going inside of them, the glowing trail went underneath. About forty or fifty yards ahead of them was a car partially covered by the collapsed wall of one side of the tunnel.
They could barely make out the shape of it but no one turned on a flashlight because as they drew closer, the dripping sound was joined by one that sounded like hundreds of soft whispers.
Moving as silently as their ninja training had taught them, the four brothers approached the rear of the car. Looking through the broken windows in the back door, they all saw a much brighter green light shining from somewhere towards the front of the car.
Leo touched Raph's arm in the dark, using the hand signal they had developed for just this type of situation. He then reached over to Don and repeated the signal while Raph did the same with Mikey.
One by one, they followed Leo into the car. Not the slightest sound did they make; all four gliding like shadows in the dark interior, their senses alive and warning them of obstructions as they practiced the way of invisibility.
The earth from the collapsed wall had come in through the broken windows and it partially blocked their path. Up ahead, the glow was growing stronger and Leo climbed on top of a seat so that he could slide through an opening between the dirt and the ceiling of the car.
His brothers followed suit and they soon found themselves standing in the passage that connected two cars together. Leo tried to slide the door into the other car open, but it was stuck.
Raph stepped up next to him and between them they managed to push the door aside.
The glow was bright enough now that they could all see where the car appeared to have been sheared in half. A drop off at the midway point in the car glowed in a pulsing rhythm, as though alive, and the whispering sound was almost loud enough to drown out the sound of the water dropping down from the tunnel above them.
Don leaned close to Leo and whispered, "They discontinued the line here because it passed under the ocean and the engineer miscalculated how far down the tunnel needed to be. The water leaking through from above made this entire area too dangerous to use."
Leo nodded, moving forward with caution. As he neared the drop off which appeared to be the source of both the glow and the sound, the turtle leader tucked his flashlight into his belt and unsheathed his weapons.
Raph was right on his tail and followed Leo's examples, the handles of his sais feeling good in his fists. It was pretty close quarters for the nunchucks and bo staff, but that didn't dissuade Mikey or Don from holding their weapons at the ready.
Reaching the ragged edge of metal, Leo leaned forward to look into what appeared to be a large sinkhole. The back half of the subway car had been held in place by tons of earth, but the front section, hanging over the drop off and sitting under the corrosive seawater, had finally broken free to plummet to the ground far below.
What he saw made him freeze in complete wonderment. Raph watched Leo for a moment before his curiosity got the better of him and he eased in next to his brother, gasping quietly at the sight that met his eyes.
Mikey waited for them to say something, glancing at Don who looked back at him, puzzled. Unable to stand the suspense, Mikey clambered over the seats until he was on the other side of Leo.
"Shell," he whispered, his eyes widening.
"What do you see?" Don asked in a low voice, trying to squeeze between Leo and Raph's shoulders.
"Rats," Leo answered him. "Hundreds of them."
"Thousands," Raph corrected, keeping his voice down so as not to disturb the nest.
His brothers moved apart far enough so that Don could look into the sinkhole. What seemed to be thousands of rats were swarming around in a nest filled with glowing debris.
Piles of old newspapers, rags, boxes and even shredded plant materials comprised the nesting area. One end of the sinkhole was quite wet, the water dripping from overhead keeping the area constantly moist.
Don tugged on Leo's arm and started to back out of the car. Mikey saw the movement and crawled over the seats to get away from the sinkhole. Raph followed along behind them, remaining completely silent.
Once the brothers were safely out of the subway cars and had put some distance between themselves and the rat colony, Don stopped.
"That was incredible," he said, clearly excited. "I wish I had my video camera."
"Don't even think about coming back down here," Raph told him, understanding his genius brother exceedingly well.
"Please tell me how a bunch of rats has a glowing nest?" Mikey asked.
"Some of them are obviously following the sewer tunnel to where it opens into the ocean," Don explained. "The junk that washes up on the shore would be great nesting material. They're dragging it to their home; that's what you saw go past us in the tunnel Mikey."
"And that makes it glow because?" Raph urged.
"The bioluminescence," Don said, "is caused by glowing plankton. They wash up to the shore with the debris and the oils that rise to the top of the water from all the pollution. That stuff forms a coating over the junk the rats pull out.
"Once the plankton die they stop glowing, but some of them survive long enough to make it to the nest where the ocean water dripping down resuscitates them. It is absolutely amazing."
"I'm happy that made your year, brainiac," Raph said. "Ya' remember that board that almost killed me and the subway car that nearly wiped us out? Ya' got an explanation for that?"
Don rubbed his chin. "The wooden post looked chiseled, but that could easily be teeth marks. I have no idea why the rats would be chewing on it unless there was something edible hiding in a crevice. I'd say the car breaking loose was happenstance as well. Probably caused by the vibrations made when the cross beam hit the ground."
"You weren't thinking the rats did those things on purpose, were you Raph?" Mikey asked in a teasing voice.
"Ahh," Raph lifted a hand and Mikey ducked aside.
Leo stepped between them quickly. "Maybe we should go back to the lair now? Master Splinter is probably wondering what happened to us."
"I'd like to suggest we brick up that hole in the tunnel wall," Mikey said. "It never seems to lead to anything but trouble."
Walking away from the rats nest and the underground subway tunnel, the four ninjas didn't notice the pair of glowing red eyes watching them from the back of the car they'd just exited.
Rats with glowing red eyes suddenly covered the area around and on top of the car. The larger set of eyes moved forward enough so that the reflection from a flashlight illuminated a partially bandaged face.
"Another time," the lipless creature promised as he watched the Turtles disappear.