The story Diego tells is about the Moon. After a comet hits the moon (La Luna), it falls out of the sky and breaks into pieces. These pieces are scattered across the ocean and on an island. With Tuga the Sea Turtles’ help and Alicia’s underwater submarine, Diego sets out on an adventure to save the moon. Without the moon, baby Leatherback Sea Turtles have no idea how to find the water after they hatch on the beach from their buried eggs.
Diego is at the beach with his parents and Alicia. They're having moonlight storytime. The family awaits their friend Tuga the sea turtle when they hear her call for help. She's been caught in a plastic bag and can't swim. Diego's parents agree to let him go out and save her with the assistance of Alicia. The two set out and bring Tuga to shore with Diego stating that the plastic bag shouldn't have been in the ocean. Now Tuga and the family is ready for Diego to tell his story about the moon.
Diego and Tuga are at the beach, waiting for the baby sea turtle eggs to hatch. When the baby sea turtles hatch, they need to find their way to the ocean with the help of the moon. Luna needs to shine her light for the sea turtles to get to the ocean. But then a comet hits Luna, which gets her to break into four pieces and fall in the ocean. Without the moon's bright light, the baby sea turtles can't find their way to the ocean. Diego can't touch the baby turtles because they need to find their own way into the ocean. Diego uses Click to find Luna's first piece.
Luna's first piece is in a cave. The other pieces are under the surface in the Underwater City, the Ocean Gardens, and the Jellyfish Cove. Diego prints the picture from Click to take with him, and Tuga agrees to help him rescue Luna.
Tuga reaches the island where Luna fell on. But when Diego enters the cave with Luna in it, the wind in the cave blows her away and into a hole. With the help of Rescue Pack who turns into a fishing pole, Diego fishes Luna out of the hole. Then he takes out a ribbon to tie Luna to Tuga. Then Diego gets a signal from Click. The baby sea turtles are crawling further away from the ocean. Diego, Tuga, and Luna need to go down to the Underwater City to get the second piece. Tuga can hold her breath underwater for a long time, and Diego needs his diving mask and air tube to breathe underwater. Diego and a few sea creatures sing mas abajo to help Tuga dive down to the bottom of the ocean.
Tuga, Diego, and Luna reach the bottom of the ocean and see a lot of fish and other creatures. A school of angelfish swims around Diego, tickling his tummy and underarms, and with him giggling "That tickles!" Soon Tuga mistakes a school of moon fish for Luna's second piece and chases after the fish with Diego following her and telling her that it's just a school of fish. Tuga apologizes for the mistake she made.
When the trio gets to the gate of the Underwater City, they are to solve three riddles. The answer to the first riddle is a leatherback sea turtle. The answer to the second is the moon. The answer to the third is Diego himself. The creatures of the Underwater City help find Luna's second piece. Then Tuga, Diego, and Luna find old sunken ships on their way to the Ocean Gardens. Tuga has to be careful because the trio could get tangled in the ropes. Soon she makes it out and to the Ocean Gardens, but the water is dark and sandy. Luckily Tuga can see the third piece underwater, but the water is wavy because the Bobo Brothers are riding stingrays. The waves are so big that they make the piece float away into a coral cage. Tuga stretches her neck to get the piece out. Now Luna only needs one more piece.
Tuga swims off to the Jellyfish Cove, but Luna is so heavy that Diego's ribbon breaks and she falls near the ocean volcanoes. Diego and Tuga can't get near them as they're very dangerous. Alicia arrives in her rescue submarine to save Luna by using her rescue rope to get her to safety. She and Diego tie the rope to Tuga as it is very strong. The quartet heads to the Jellyfish Cove. The stinging jellyfish are in front of the last piece. Tuga manages to eat all ten jellyfish and dig the piece out. Now that Luna is full, she can go up back in the sky to glow for the baby turtles.
When the quartet heads to the beach, they are informed that orcas are coming, which leatherback sea turtles are afraid of. Luna, Tuga, and the kids head to a cave to hide in. When they get to the beach, the baby sea turtles are lost. Alicia and Diego manage to get Luna back into the sky and encourage her to glow. The baby sea turtles safely get to the ocean.
Mami and Papi have enjoyed their son's story. Luna is a little skeptical about breaking like in the story, but she really can't; Diego only made it up. Baby sea turtles do the moonlight to find their way into the ocean, and the leatherback sea turtles can do all the stuff in Diego's story, like swim, crawl, and dig. Tuga, Luna, and the rest of the family have really enjoyed Diego's story.
- First TV special where Diego's parents appear