The Tracy family watch the launch footage of the Sun Probe, a rocket which blasted off a week ago and is on a mission to collect matter from the sun itself. Brains isn't too interested, having already learnt the mission off by heart. Inside, he concentrates on working on Braman, a robot he's constructed. The Sun Probe fires off the probe, which collects the matter successfully. It then reattaches itself to the front of the rocket.

However, the Sun Probe becomes locked on a collision course with the sun. Radio beams from Earth fail to reach the ship due to the sun's radiation and heat, leading to the staff at the launch site contacting International Rescue. Knowing that this is going to be a tough one, the Tracys decide to put two plans into action. Alan, Tin-Tin and Scott blast off in Thunderbird 3, with their plan being to use the ship's safety beam to get the Sun Probe to fire its retros.

Virgil and Brains are to head out in Thunderbird 2, and use a transmitter truck to send a powerful radio beam from Earth. Virgil finds the best place to be, so they load up Thunderbird 2 with a mobile computer, and then fly towards the Himalayas. In Thunderbird 3, Tin-Tin tries to use the safety beam, but it's out of range of the Sun Probe. Alan says they've got no choice but to get closer, despite the danger it posed to themselves. Thunderbird 2 arrives in the mountains, and Virgil and Brains head out in the transmitter truck. They try their radio beam, but it's not powerful enough.

Thunderbird 3 has to move much closer to the sun than expected. Alan tells Tin-Tin to try boosting the power to the safety beam, which she does. The beam reaches the Sun Probe, allowing its retros to fire. It turns away from the sun, and heads back to Earth, with the 3 solarnauts inside it all saved. However, Thunderbird 3's retros then also fail to fire, resulting in the ship now being in a collision course with the sun. Alan realizes the power boost is what has caused this, but he and the rest of the crew pass out due to the heat before they can switch the beam off. News of Thunderbird 3's fate reaches Jeff, who reports it to Virgil and Brains. Brains believes he can use the truck's beam to get Thunderbird 3 to fire its retros, so he and Virgil go to get the computer. But then they realize they've brought the wrong box -instead of finding the computer, they find Braman!

Brains is able to use Braman and get him to work out the frequency they need. Brains and Virgil head back to the transmitter truck, and use its beam to reach Thunderbird 3. The ship's retros fire, saving it and allowing it to turn around and head back to Earth. With the crew saved, Jeff tells Virgil and Brains he's really proud of his International Rescue team today.

Sometime later, Brains says now the excitement of Thunderbird 3's homecoming is over, he wants to see if his improvements to Braman have worked. Braman plays chess with Brains, managing to put his opponent in checkmate. Brains can't believe that a machine could have a better brain than him, but Jeff assures him it was just a fluke -he has been working kind of hard recently. He, Alan, Tin-Tin and Scott all thank Brains for his work, and then Braman also chimes in by thanking Brains.

Notes

-The subplot where Thunderbird 3's retros fail to fire was not in the original script. It was added to extend the episode from 30 to 50 minutes. The Sun Probe launch sequence was also apparently something added.

-During the opening teaser, there is a shot of Brains and Braman which is never used in the episode itself.

-The robot's name is pronounced "Brayman" and not "Brarman". The script does specifically spell it Braman though. Braman will make a few more appearances in the series.

-When Scott goes into Brains' lab, he stands in front of a drawing board with some pictures on it. These pictures are actually real pieces of concept art which show early versions of Thunderbird 1 and Thunderbird 4 -the most obvious difference is the markings on Thunderbird 1, which show "R1" on the wings. The "R" stands for "Rescue" -the pre-production name of the series. The concept art of Thunderbird 4 clearly says "RESCUE" on it.

-Jeff mentions Grandma Tracy in this episode, although she is not seen. In theory this episode has to take place after Move - And You're Dead.

Errors

-This drawing seems to suggest the cockpit of the Sun Probe is within the probe itself, but in reality it's in the rocket.
-Brains has a little device that initially has a yellow light bulb on it. When this device is seen later, it now has a blue light bulb. A little later on, its gone back to having a yellow light bulb again.
-Colonel Benson is, for the most part, voiced by David Graham. But for his call with Jeff, he's voiced by Ray Barrett.
-During Benson's call with Jeff, the machine Jeff uses physically moves to the right slightly when the screen changes from "SOUND ONLY SELECTED" to "END OF CALL".
-When the sofa moves down, Alan is on the left, Scott is on the right. But the shot showing the miniatures have Scott on the left, and Alan on the right.
-Due to the use of stock footage, Thunderbird 2 seemingly selects pod 3. But when it lands in the mountain later, you can just about make out that the number 6 is on the pod's door.
-When Virgil tells Jeff how it's pretty stormy, we then see this shot of Thunderbird 2 covered in snow. This is then immediately followed up with this shot, and the snow on Thunderbird 2 has disappeared.
-Moments later, we see this shot of Thunderbird 2 covered in snow. A few seconds after this, we then see this shot, and the snow is missing again.