"Shit! Shit! Where did it go?" Raph yelled; his lips curled back from his teeth, mouth open as he sucked air into overworked lungs.

Don glanced at his brother and then turned to look into the darkness of the underground tunnel, heart thumping in his chest as he fought to catch his breath. "Down there I think. I saw movement."

"Donny, where's your bag?" Leo called as he stepped carefully over rocks and soil, his katanas out.

"I lost it when the ground gave way and dropped us here," Don said. "I think it's under a pile of dirt."

"We're lucky we aren't under a pile of dirt," Mikey said. "I've never seen anything move so fast, not even those things that Bishop mutated."

"Anybody get a good look at it?" Leo asked.

"No." Raph was on the opposite side of the wide tunnel, his sais gripped tightly in hands that stretched out to either side of him. He was poised, edgy; body coiled and ready to spring at the first sign of the thing they'd been chasing. "It's big though," he added.

Leo, Raph, and Mikey moved in a spread out line, slowly walking towards the darker section of the tunnel, Don just a few paces behind them. The thing that had destroyed Don's sensors and set off his alarm system had led them on a merry chase, but they still weren't sure what they were dealing with, so they stayed cautious.

Something felt wrong about the tunnel they were in and Don stopped for a moment, reaching out to touch the wall. The earth looked packed, compressed; as though something had pushed against it hard enough to squeeze the oxygen out. It was almost too warm to comfortably touch and when Don pulled his fingers away, a bit of mucus like slime was adhering to them.

"This tunnel is new," Don said as his eyes drifted up to the ceiling and then to the ground beneath his feet.

Leo stopped moving and signaled for Raph and Mikey to do so as well. "How new?" he asked, his voice low.

"Too new," Don said with a hint of warning in his voice. "Like in the last thirty minutes new."

Raph's eyes met Leo's across the intervening space. Sudden understanding made them widen their eyes simultaneously.

"Out of here," Leo barked the command. "Now!"

Mikey spun on his heel, darting back towards Don. He could hear the other two coming fast on his heels, urgency pushing aside their usual silence.

The brothers managed ten more yards before a deafening roar began to echo in their eardrums, followed by searing pain.

Then total blackness descended on all four.