In England, a large fire has started at a mine. International Rescue are on the scene, and are helping out the local fire crews in putting out the blaze. Thunderbird 1 and Thunderbird 2 have landed near a house in the countryside.
Inside the house, a young boy called Chip Morrison is all excited that International Rescue are here, and wants to know what they are doing. His father explains that they are going to go down the shaft and bring up the trapped men below. He asks his son to go to sleep, and then leaves the room. After he is gone, Chip can hear the explosions outside, and stares out of the window at Thunderbirds 1 and 2.
Later on, the fire is under control, so International Rescue are no longer needed. Scott returns to base and lands Thunderbird 1, whilst Virgil and Alan are also on the way back in Thunderbird 2. Virgil says that Thunderbird 2 has developed some kind of electrical fault, so Jeff tells Brains to check it out later. Thunderbird 2 lands and reverses back into the hangar.
A warning alarm sounds, and Jeff tells Virgil to not release the pod. He gets Gordon to go and find Scott, and to meet with him in Thunderbird 2's hangar. Virgil and Alan can only wonder what is wrong as Jeff appears, holding a gun.
Jeff tells Scott and Gordon to cover the pod door. He then tells Virgil that there is a saboteur on board, and he can release the pod now. Thunderbird 2's legs activate. Scott and Gordon are ready with their guns, as Virgil opens Pod 1's door.
Jeff calls out through a loudhailer: "All right, we know you're in there! Come on out, or we're gonna blast you out!"
A frightened child's voice replies: "Don't shoot...please don't shoot! I didn't mean any harm!" The 'saboteur' is none other than Chip.
Jeff is angry with his sons, saying this shouldn't have happened as the International Rescue vehicles never should have been left unguarded. This boy is a security hazard, and they need to return him to his home — but he's seen all of them, and knows their location. They've got to think of a way to get him out of there without the boy being a security risk. Jeff then finds out Chip is currently being looked after by Virgil — Jeff hopes Virgil is keeping his mouth shut. Meanwhile, in Thunderbird 2's hangar, Chip is looking at Thunderbird 2, amazed by the size of it. He asks Virgil if he is the one who gets to fly it, but Virgil says they have very tight security here and he can't say. Chip says he understands, and tells him that when he grows up, he wants to be a member of International Rescue. Except he'd like to be the pilot of Thunderbird 1, because he thinks it is the fastest Thunderbird, and the most important one. Virgil says that without Thunderbird 2, none of the rescues would be possible! Take the time they saved Eddie Houseman...
Chip says he wished he could have been there. Alan then enters and says Jeff wants a word with Virgil. Virgil leaves, leaving Chip in Alan's care. Chip says he liked Virgil, as he told him all about Thunderbird 2. Alan says Virgil shouldn't have said anything, and he won't be getting any information out of him about Thunderbird 3. Chip excitedly exclaims that Alan must be the pilot of Thunderbird 3, and Alan realizes he's just blundered already.
Alan takes Chip to Thunderbird 3's hangar, and they look at the rocket from the very bottom. Chip says this must be the spaceship, and wonders how fast it can go. Alan says he can't say, and Chip says he guesses that Alan, being a spaceman, probably doesn't get to be as involved in the rescue operations. Alan says that's not the case — once Thunderbird 3 is up in space, he's in charge! Does he remember that Sun Probe rocket that went out of control and was on a collision course with the sun?
Chip says Alan really is a member of International Rescue. Scott them comes in and says Jeff wants a word with Alan. In the Tracy lounge, Jeff is still shouting, saying that this is an impossible situation. Alan comes back and says he left Chip with Scott in Thunderbird 3's silo. Jeff is angry Chip has been shown Thunderbird 3, but is glad he is with Scott.
"Well at least he's with Scott now, he won't get anything out of him."
Scott says he remembers their first mission. His brother John radioed in from the space station that Tin-Tin's aircraft, Fireflash, had a bomb planted in the landing gear by a saboteur. So he dashed off to London Airport and set up his Mobile Control Centre in the control tower.
Chip says he could picture the whole thing in his mind. Now all that's left to see is Thunderbird 4. Scott tells him not so fast — he's been told too much already, and there is no point in him looking all disappointed. The answer is no; he is absolutely, definitely not seeing Thunderbird 4.
A short time later, in Pod 4, Chip is at the controls of Thunderbird 4. He says it is a bit smaller than the others, and whilst Gordon agrees, he says it is still a very necessary part of International Rescue. He's involved in all kinds of rescues, but he can't tell Chip about them. But Chip thinks he knows the kind of rescues Gordon would be at, such as that one at the Allington Suspension Bridge. Gordon is surprised Chip remembers that. Who'd have thought that an underwater craft would have been used to save a Martian Space Probe rocket?
Chip has gone, and Scott, Virgil and Alan don't know where he is. Scott thinks their father will go even more berserk if he finds out the kid is roaming the base, so they'd better start a search. But Gordon tells them to come over to where he is, and to take a look. They see that their father is casually telling Chip, who is sitting at Jeff's desk, about how a rescue operation can take quite a bit of organizing, and he controls the whole mission from his desk. All Jeff needs to do is press one of these buttons, and Thunderbirds are go!
Later on, Jeff, his sons and Brains gather together to discuss what they are going to do. They need to get Chip back to his home and prevent a security leak. Jeff comes up with an idea: Chip is from England, a place almost on the opposite side of the Earth from their base. It will be night time in England but daytime here, and Chip will have been up for around 24 hours — meaning he'll be very tired. They will put him to bed now, and do so.
They then transfer his bed into Thunderbird 2. Thunderbird 2 takes off, and heads to England. Chip managed to get out of his house undetected, and Scott and Virgil manage to get into it likewise. They put Chip into his own bed, and then leave — all before dawn breaks. Jeff thinks that when Chip wakes up in his own bed in his own home, he will believe that his adventure on Tracy Island was just a dream.
Chip's father returns from the mine, as the disaster is over. Chip wakes up, as his father tells him what a fantastic organization International Rescue are. Chip says he knows all about them, and just wait until he sees their bases and machines. His father says he must have been dreaming again, and Chip says that must have been the case — although it seemed so real. Up in the air, Scott reports that their mission has been completed, and the security hazard is negative.