Notes from the Underground, Part 1

Donatello was examining some crystals they found in the new lair while Michelangelo was watching a monster movie. Once the movie finished, Mikey started bothering Don. He picked up two of the crystals and hit them together. They produced a high-pithed tone. Little did they know that they woke something deep underground.

Along with creatures underground, the noise also woke Splinter, Leonardo, and Raphael. As Don explained he didn't know what was causing the noise and light, the perimeter alarm went off. When they got to the site, all they found was weird tracks and evidence that someone had been eating through the rock. Don took a sample of the melted rock and everyone went back to the lair. No one noticed a pair of eyes watching them.

After analyzing the rock at the lab, Don concluded that the rock was melted by a powerful chemical. Splinter suggested they investigate further. All the Turtles were excited at the prospect of an underground adventure except Mikey, who was still freaked out by the monster movie.

The Turtles followed the tracks to an abandoned subway station from the 1900s. The place was in bad shape and a loud noise seemed enough to make the tunnel collapse. The Turtles didn't spot a creature following them. The creature roared, causing the tunnel to collapse and the Turtles just made it.

Shortly after, the Turtles made camp. Shortly after going to sleep, they were under attack. A creature rolled a giant boulder toward them. They were able to grapple across a deep chasm to escape.

After looking around their surroundings, the group found a high tech door that was forced open. Inside, they find an abandoned genetics lab. Mikey accidentally set of the security system. A force field that permitted no living tissue through was activated, threatening to crush the Turtles. Raph was able to deactivate it by knocking it's energy crystal out of place with his sai.

Don took a look at a computer, which had a video diary. The video revealed that the lab was established by the Shredder who believed he had enemies deep underground. The Foot mutated "volunteers" into creatures capable of tunneling deep into the Earth. The mutants became uncontrollable, killing all the Foot staff.

The Turtles decide to head back to the surface, but find three creatures blocking the way.