At Tracy Island, Nicky asks Santa -who is Jeff in disguise -for his wish. He asks to see all the Thunderbirds launched, but Jeff says he can only see one. Nicky decides to see Thunderbird 3 blast off, which he is wowed by. Jeff tells him the story about what it took to get him to the island, which all started a several days before Christmas. At the Coralville Children's Hospital Committee, an agreement is reached to raise money for a new solar therapy wing: Saunders of Saunders Automations will provide a rocket, whilst Harman, a store owner, says he will fill with toys. This rocket will then be sent to the hospital and one of the presents will have an invitation in it for the receiver to visit International Rescue. A test rocket is later launched to the hospital.

The rocket drops a canister, which falls onto the hospital grounds after deploying a parachute. Nurse Nimmo checks it and sees that a porcelain horse inside one of the presents hasn't been damaged in any way, so the test is a success. At Tracy Island, Jeff tells everyone he wants this operation to be taken as seriously as any other. The family start to make preparations for Christmas, including preparing lots of food and putting up decorations. On Christmas Eve, two thieves called Scobie and Straker go to Harman's store and tie up two Santas.

Next door to Harman's store is the Second National Bank. Two security guards test the alarm, which consists of a floor that sets the alarm off if anything touches it. As they leave, Scobie and Straker cut a hole in the wall and set up a cable, which Scobie uses to enter the vault without stepping on the floor. He gets pulled across to the opposite end of the room by Straker and starts to take millions worth of gold bars. Straker then pulls him back.

The thieves believe they've gotten away with it and are about to leave when they accidentally cause something to drop onto the floor, setting the alarm off. Desperate to escape, they steal the Santa costumes then run to a freight elevator, which has a single canister inside it. Not knowing what it's there for, the two get inside it and close the door, seconds before the elevator moves up. The canister they're in is placed into the waiting rocket, which then takes off.

The canister is dropped off safely, but Doctor Lang pulls out a gun and tells the others that he'll open it. He reveals he had been tipped off by the police, and when he opens the doors, they find Scobie and Straker inside it, alive but unconscious. A reward had been put out for their arrest, which the hospital will now get as they were the ones who found the thieves.

At Tracy Island, Nicky enjoys his time with the Tracy family. Brains then says he has a surprise party piece for everyone. He presses a few buttons on a box, which causes several devices outside to shoot out fake snow, covering the house and part of the beach. Jeff tells Brains that he's given them a real old-fashioned Christmas.

Notes

-Usually new episodes of Thunderbirds were broadcast once a week, but there was a several week gap between this one and the previous one, presumably to allow this Christmas themed episode to air on Christmas day.

-However there was a movie released between this episode and the previous one: Thunderbirds Are Go premiered on December 12th, 1966.

-The toys of Thunderbirds 1, 2, 3 and 4 seen at the start of the episode were actual toys which were available to buy at the time, created by J. Rosenthal Toys. This company made a Thunderbird 5 toy as well, but it doesn't appear in the episode.

-The footage showing Alan getting into Thunderbird 3 was shot for Thunderbirds Are Go.

-This is the only second season episode that Kyrano appears in.

-The calendar Tin-Tin takes a page off states it's the year 2026. This has caused a lot of debate in the Thunderbirds fandom over when the series is set, some say 2026, but others say 2065.

-This is the final episode of the show. It was suddenly cancelled due to ITC founder Lew Grade failing to sell the series to any American TV network. Some fans believe that more episodes may have been in production and had scenes filmed, others believe at least some scripts would have been written, but as of 2024 there is no proof of any of this.

Errors

-When Brains tells everyone they can open their eyes, a decoration can be seen falling off the Christmas tree behind Nicky.