Return to the Underground
Teenage Mutant Ninja Turtles (2003) episode
Return to the Underground.PNG
Season Code: S02E13
Episode: 39
Original airdate March 6, 2004
Written by Marty Isenberg
Supervising Producer Lloyd Goldfine
Producers: Gary Richardson
Frederick U. Fierst
Al Kahn
Norman Grossfeld
Thomas Kenney
Supervising Director  Chuck Patton
Story Editor: Michael Ryan
Episode chronology
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"What a Croc" "City at War, Part 1"

Teenage Mutant Ninja Turtles Season 2
November 8, 2003 - October 2, 2004
List of Teenage Mutant Ninja Turtles episodes


  1. Turtles in Space, Part 1: The Fugitoid
  2. Turtles in Space, Part 2: The Trouble with Triceratons
  3. Turtles in Space, Part 3: The Big House
  4. Turtles in Space, Part 4: The Arena
  5. Turtles in Space, Part 5: Triceraton Wars
  6. Secret Origins, Part 1
  7. Secret Origins, Part 2
  8. Secret Origins, Part 3
  9. Reflections
  10. The Ultimate Ninja
  11. The Return of Nano
  12. What a Croc
  13. Return to the Underground
  14. City at War, Part 1
  15. City at War, Part 2
  16. City at War, Part 3
  17. Junklantis
  18. The Golden Puck
  19. Rogue in the House, Part 1
  20. Rogue in the House, Part 2
  21. April's Artifact
  22. Return of the Justice Force
  23. The Big Brawl, Part 1
  24. The Big Brawl, Part 2
  25. The Big Brawl, Part 3
  26. The Big Brawl, Part 4

Season 1Season 2Season 3Season 4Ninja TribunalFast Forward - Back to the Sewer

"Return to the Underground" is the thirty-ninth episode of the animated series Teenage Mutant Ninja Turtles, which originally aired on March 6, 2004. It had 1.22 million views on the 4kids website as of 2007.


Major Characters

Secondary Characters

Main Locations, Vehicles and Accessories


Voice-Over Introduction

Donatello: A while back, I made a promise to some friends... and, believe it or not, that thing struggling in the net right now is one of those friends. You see, it's kind of a long story. Our friends were mutated into monsters by The Shredder's scientists; now, they're forced to live underground, prisoners of an ancient city powered by a giant crystal moon. And I believe it's these very same special crystals that are the key to saving our friends, and hopefully curing them for good. Trouble is, right now, my friends don't particularly want to be cured.

Plot Synopsis

Open on Donatello examining some of the underground crystals that the Turtles found in Episodes 13-15, trying to find a cure for the people who had been turned into monsters by the Foot geneticists.

Exhausted after having been up for days studying the crystals, he falls asleep and dreams of the underground city where the monsters now live. Quarry, in her human form, is in the dream, then changes into her monster form. The Crystal Moon liquifies and covers Quarry, she emerges in her human form and gives Don a clue - "hear the crystal." Waking up, he finds that the clue works – the crystals react to sound and turn into liquid when exposed to heavy sonic bombardment. Donatello hopes to use the crystalline liquid as an antidote serum to cure the people of their mutation.

The gang decides to head underground to help the monsters. Don leads the team to his lab, where he unveils his latest creation, the Turtle Tunneler. This vehicle can burrow straight down into the earth via a huge, front-end drill. The guys pile into the snazzy new ride and tunnel their way back to the underground city. However, once they arrive, they discover that the crystal “moon” that had floated above the underground city the last time they were here is gone!

Not only is the crystal moon missing, but the underground city is now populated with dangerous mutants. The crystal moon, Donatello reminds us, was the only thing that allowed the monsters to return to their human forms - without the moon, they all reverted to their hideous forms. The Turtle Tunneler is attacked by the spider and insectoid-dragon mutants. Don tunnels through a wall and escapes the monsters, but once they arrive on the other side, two more creatures lift the vehicle up and toss it over the ledge, where it plummets into a river of lava far below!

The Turtle Tunneler safely emerges from the molten rock (Don notes that the vehicle is lava-proof), but the guys are stalked by monsters as they make their way inside the city. The Turtles disembark and locate the still-frozen body of The Entity (see Episode 15). Donatello removes the crystal from the pedestal and a wall mysteriously opens up to reveal a hidden area. The Turtles enter the room and find more bodies being held in stasis fields - apparently the Entity was lying when he told the TMNT that he was the sole survivor of his race. The guys hear approaching creatures and Don uses the crystal to close the door, but it doesn't hold up to the assault and crumbles away. In leaps Quarry… but she's not happy to see the Turtles!

Using the weaponry encased in their tech packs, the Turtles shoot concussive stun blasts at Quarry while Donatello prepares to inject her with antidote serum. Raph manages to pin the menacing mutant to the ground and Don injects her with the cure. Thankfully, Quarry reverts into her human form and introduces herself as Sydney. We learn that the people who were forced to live underground grew tired of their life and decided to try to create their own antidote. The group needed more crystals to study, so they used explosive geodes in effort to knock some shards loose from the moon high overhead. Unfortunately, the "bombs" were too powerful and the blasts that they created caused the crystal moon to fall into the lava bed! This event plunged the underground city into darkness and everyone returned to their monstrous forms.

Don comes up with a plan to raise the crystal moon out of the lava. He will use the Tunneler to tie a crystal cable around the moon, and then the others can use the explosive geodes to topple a tower in the city. As the structure falls, it will pull the cable and raise the moon - so it will act as a gigantic winch. Sydney rides with Don in the Tunneler to navigate their course as the rest of the team surrounds the base of the tower with explosive geodes. Sydney leads Don directly to the crystal moon and he begins to wrap the cable around the giant gemstone. Meanwhile, the other three Turtles find themselves face-to-face with numerous mutants and spend their time dodging and repelling attacks. Eventually the spider mutant manages to capture them in its weird webs!

Don and Sydney tie-off the crystal moon as the ship's heat shields begin to fail. Donatello radios his brothers to set off the explosives - but the others are still "tied-up". Leonardo manages to cut out of his cocoon and frees his brothers, as the mutants close in on them. Mike uses his tech-pack's grappling ropes to swing away from the threat and set off the explosives. The tower falls, pulling the cable, which drags the crystal moon out of the lava! Donny's plan worked!

The crystal moon's power begins to work immediately, and the monster mutants revert to their human forms. Leo radios Don to tell him the mission was a success - but there's no answer! It looks like Don and Sydney couldn't escape the lava before their shields gave out. Mike, Leo and Raph walk over to the lava, afraid that they've lost their brother - but the molten rock begins to bubble and the Turtle Tunneler comes shooting out! Don and Sydney have survived!

The brainy ninja and his assistant then get to work on the crystals that they've recovered and make enough antidote to cure everyone. The TMNT then lead the people back to the surface, arriving topside just as the sun is setting. Sydney looks at the sky and sheds a tear of joy to see such a beautiful sight. She thanks the Turtles and the humans make their way into the city.

The TMNT begin jumping down the open manhole cover, but before Don can dive in, Mikey pops out and says that while Donny can sometimes be a pain in the shell, he's proud to be his brother. Donatello leaps into the hole with a huge, satisfied grin plastered on his face.


(as the Tunneler emerges from a lava pit, and the others have varying expressions of shock of their faces)
Donatello: What? You think I wouldn't have designed this thing to withstand lava? What kind of idiot do you think I am?
Michelangelo: Are there different kinds?!

Michelangelo: Nets! I'm all out of nuts! ...I mean... Nuts! I'm all out of nets!

Michelangelo: Him and his big ideas! "C'mon guys, lets go down to the underground city! We'll have some laughs!" We'll get EATEN!!

(Mikey jumps into sewer but holds onto the rim of the hole)
Michelangelo: Don, you might be a pain in the shell, but I'm proud that your my bro!

Sydney: My real name is Sydney.


  • Second appearance of the Underground, Quarry, Stonebiter, and Razorfist.
  • Quarry's real name is revealed to be Sydney. In "Notes from the Underground", they asked Quarry if it could remember, but all she could say was the S sound.
  • Similar to the scene in "Notes from the Underground" Quarry is changed back into an attractive human girl, but due to having previously been in monster form she is naked so the camera only shows her from the shoulders up. When the other monsters are changed back into people, they too are naked and only viewed from the shoulders up.
  • Donatello's line "Gentlemen, and Mikey" is reused in the 2012 series as "Gentlemen, and Raphael."



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