It's Christmas time for the Octonauts as they travel to Professor Inkling's home, the sea mount (An underwater mountain) until an undersea tremor shakes the sea mount as Inkling discovers that his friends and his nephew,Squirt are trapped inside the sea mount as Tweak brings out Captain Barnacles' present, the Gup-X, the strongest, yet biggest Gup ever. They also learn about Christmas tree worms which live in holes in rocks and they keep asking Captain Barnacles if it's Christmas yet (a running gag in the Christmas special). The Golden Coral is also trapped, and she thinks she'll be spending Christmas upside-down. She is also 500 years old. After successfully completing the mission, it all ends with a grand Christmas musical number and everyone wishes the audience, "Merry Christmas!"
- Octonauts Wiki: The Great Christmas Rescue
- "The Great Christmas Rescue" at the Internet Movie Database