Soon after, the Turtles found themselves on wheels—just not the kind they were expecting.

“This … is not … awesome!” Raph moaned.

He and his brothers were all working up a sweat, pedaling exercise bikes to help propel Donnie’s latest and greatest creation: the Turtle Sub! The submarine, designed to look like a giant sea turtle on the outside, creaked under the pressure of the East River as they piloted it thirty feet below the surface.

“Seriously, Donnie?” Leo said, huffing as he pedaled. “A submarine powered by bicycles?”

“You know what would have been more efficient?” Raph asked, straining. “Swimming!”

“Hey, pipe down, guys!” Donnie was clearly insulted. “Kinetic energy is the only way to charge the engines,” he explained. And then, reaching up to a console of switches, he added, “Which should be done right about now!”

With the push of a button, the Turtle Sub’s engines suddenly hummed to life. The Turtles, spent and exhausted from their marathon of pedaling, sat back to recover and catch their breath.

Except Donnie. He was at the helm, steering the armored Sub through the murky depths toward a Kraang signal he’d been tracking.

After a few moments, Leo gathered whatever leftover strength he had and dismounted from the bike. “We’re almost there,” he said gratefully. He collected himself and took the role of captain. “Up, periscope!” he commanded.

A ramshackle periscope, constructed from camera parts and an old toilet seat, swung down from the rafters. Leo winced at the stains caked on it. He did not want to put his face on that.

Unfortunately, it was the only periscope on board.

With a scowl, he leaned in, careful not to touch the toilet parts. He looked through the viewer at the underwater scenery ahead.

The East River was a mysterious mix of moving light and shadows.

Well, one very big shadow—a misshapen form that disappeared and reappeared, circling the Sub. It moved quickly, scissoring the water with what looked like a pronged tail.

“Uh, Donnie?” Leo called from the periscope. “Any chance this Kraang facility looks like a giant sea mutant?”

Donnie looked through a porthole and saw the creature for himself. “Oh, that’s not a mutant,” he said flatly. “Based on his physiology, I’d say the Kraang brought him here from Dimension X.”

Leo shuddered. Another alien?

“How is that less horrifying?” he asked.

“It’s not,” Donnie replied nonchalantly. “I just like to be accurate.”

Raph stepped up to the periscope to see this beast for himself. It looked like an underwater dinosaur, with its long serpentlike tail, massive stomach, elongated neck, and tiny head that flashed rows and rows of sharp fangs.

“Well, whatever it is, it looks like it’s guarding that,” Raph said, nodding to a strange domed structure anchored to the seafloor.

Raph had spotted the Kraang’s underwater facility!

Inside the Turtle Sub, Leo turned back to his brothers. If they wanted to infiltrate the facility, they’d have to sneak by that giant beast.

“Let’s go stealth,” Leo commanded.

At nearly a hundred feet below the water, the Turtles deactivated every light on the Turtle Sub. The hull around them was cast into complete darkness.

They were swimming blind.