A helijet flies through the sky. Inside it is a news crew, and presenter Eddie Kerr says that they are now flying at 3,000 feet. They're up here to show everyone a really fantastic sight. As the helijet continues onward, a building comes into view.

This building is the newly completed Thompson Tower, and Eddie says they will fly down vertically and go past the sea of windows. As the helijet heads down, Eddie says that Thompson Tower is open for the first time today. It's more that just a gigantic multiple store. It's a completely self-contained city, and every single item produced in the entire world can be obtained somewhere in the 350 floors. A person could live a whole year without moving from one of the rooms of the 12 hotels housed in the tower. The building is half a mile wide and 2 miles deep, it's a stupendous feat of engineering skill and commercial achievement. Beneath the great structure is parking space for 10,000 automobiles, and a 4 mile long monorail links the parking area with the store.

At Tracy Island, Scott and Virgil are testing a new cutting gas called oxyhydnite. They are being watched by Brains, Jeff and Tin-Tin, and everything seems to be going well so far. Jeff tells Brains that if this gas is as good as he says it is, it'll help their work tremendously. Brains says they're still in the experimental stages, and they don't know what the effect the mixture will have on the operators. Jeff reminds his sons that at the first sign of trouble, they must get themselves out of there. Scott and Virgil continue to work.

Jeff thinks the gas is amazing, as it has cut through the steel door 3 times faster than a laser beam -looks like Brains has done it again. Brains thinks it's a little early to tell, but the signs are favorable. Jeff tells Scott and Virgil to cut a panel large enough to get through, and then they'll call it a day. Tin-Tin then reports that Virgil's blood pressure has risen slightly. Jeff asks him if he's ok, and he says he is. Jeff asks Brains why the rise? Brains thinks it could be normal reaction to concentration. Scott's blood pressure then also rises.

Virgil suddenly starts wobbling, and becomes unresponsive. Jeff tries to contact them, but neither of them respond. Virgil then falls over backwards, so Jeff tells Brains to turn the gas cylinders off. Scott then also falls down. Jeff tells Tin-Tin to prepare the sick room.

Later on, Brains says he has the results of the tests. Jeff asks what went wrong, was it the masks being faulty? Brains says no -he checked them, and they were perfectly sound. Scott and Virgil are physically ok, but the blood samples show positively that the gas entered through the pores of the skin. Jeff asks if there will be any after effects, but Brains says no. Virgil then wakes up, and says he feels great. But he wonders what he's doing in the sick room. He then remembers feeling dizzy, and guesses he must have passed out.

Scott then wakes up, and thinks that was a good sleep. He asks what all the bedside manner stuff if, and Tin-Tin explains that he passed out in the test chamber. Brains says he'll get back to the lab, and get to work on the oxyhydnite again. Virgil asks if they can get up, and Jeff tells them alright -but they need to take it easy.

The Carter family are on the way to Thompson Tower, but come across a bad driver in the way. Joe starts using the horn, but his wife Blanche tells him to stop -she's probably just learning to drive. Joe thinks the driver ahead is a danger to everyone, but then the highway patrol shows up. They pull the driver over, and Joe thinks she had that coming -people like that cause accidents, they're a menace. Tommy Carter then sees a large building up ahead, and asks if that's it. Joe says that's it.

Blanche sees the auto park entrance, but thinks it's such a long way from the store. Joe says the park covers a big area, and then drives his car down the ramp. They park, and Joe says they'll go and see the store. Blanche wonders how they get there, and Joe says they'll follow the sign pointing towards the monorail.

Outside, the bad driver complains that patrol car who stopped her had some nerve. Her husband tells her to forget it, as she only got a ticket. He tells her to concentrate on what she's doing, but as she drives to the auto park entrance, she's going too fast. He tells her to slow down, but she panics and ends up hitting the accelerator harder, causing their car to smash through a barrier. The car ends up crashing into another car.

The guy tells his wife to get out of the car, as it's on fire! They head towards an emergency exit, as the car explodes. This quickly causes a chain reaction, causing several other cars to explode. This causes large parts of the car park to be set ablaze, and the fire continues to spread.

The carter family hear some rumbling, but Joe says right now they need to find out which way to go to get to the monorail. He thinks it's like a rabbit warren down here, but Blanche thinks he should have bought a guidebook. Meanwhile, outside Thompson Tower is another building called the control tower. The fire gets picked up there, and the controller tells his assistant to check all sprinkler systems and alarms. The assistant says the sprinkler systems are negative, and the emergency systems aren't responding either. The controller says to alert all fire appliances, as they must contain the fire to the sub-basement. He wants all the corridors there shut down.

The assistant starts using cameras to check that the corridors are clear, and then seals then off. Nearby, various emergency services start to move out. The controller has the emergency services directed to section 12, so the people in the tower won't see them. It's vital that they don't scare anyone, and if they're lucky they won't be needed.

Tommy thinks his mom and dad sure take their time. As they look at a map, he tells them he's going to hide, and bets they won't find him. Joe says that will, but Tommy enters another room. Joe and Blanche enter the room and say this is the police. They're coming in to get him, and tell Tommy the place is surrounded. Tommy says he'll come quietly.

The assistant checks that corridor D-50 is clear, and then seals it. As the Carter family leave the room, Blanche says now they need to find a way out of this maze. But Joe then realizes that they can't go that way, as it's blocked. But they then realize that the other end is also closed. They've been shut in, and Joe wonders what's going on.

The assistant says all the corridors have been checked and sealed. The controller says they can contain the fire in areas 1 and 2. The assistant thinks the fire will burn itself out, but the controller says to have the fire tenders standing by just in case. The assistant tries to use the main vent seal, but it fails to operate. They realize the fire has spread to the tower, so the controller tells him to alert the fire tenders and get to work on that vent shaft.

The fire tenders move in towards the tower. The assistant says the air vent seal can't be shifted, as the cover is jammed. Flames are now going up the building. The controller says to have the fire tenders moved in, as they can't wait any longer. The assistant thinks the people in the tower will panic if they see 20 appliances screaming towards them. The controller thinks they'll see nothing at all if those flames are not put out. Inside the corridor, Joe starts banging on one of the doors, demanding to be let out.

The Carters then see smoke coming through the bottom of the door. Joe realizes the place is on fire, and they've been shut in. Parts of Thompson Tower are now on fire. The controller and his assistant are getting sections of it evacuated, but are then contacted by the fire chief. He tells them that all pumps are operational, but they aren't holding the fire.

Blanche asks why they aren't being let out. Tommy asks where the smoke is coming from, but she tells him not to worry, as they'll be out soon. Joe keeps banging on the door and screams for help. The assistant confirms more sections have been evacuated, so the controller says to check the cameras to see if the fire has spread.

The assistant soon finds the Carters in corridor D-50. He wonders how they got in there, as when they checked all the corridors earlier, they were empty. The controller says three people are in there now, and they've got to get them out. The assistant thinks that's impossible, no one can get near the sub-basement entrances. The camera feed then cuts out, and neither the controller or assistant know what to do. Tommy asks if they're going to die, and Blanche says of course not. Joe says someone will come and rescue them.

At Tracy Island, Alan asks how Scott and Virgil are feeling, as that gas is mighty strange stuff. Scott says Brains is working on it, but the funny thing is he feels better than normal. Virgil agrees, and hopes Brains can iron out the snags. He thinks that new cutting power could be useful, but Alan thinks it won't be if it knocks you out each time you use it. He asks Tin-Tin how the water is, and she says it's just great. She wants him to come in, but he says he hasn't the time. He has to get ready to relieve John in an hour, as his term of duty in the space station is over for another month. Tin-Tin thinks it'll be nice to see him again, as he must get lonely up there.

In Thunderbird 5, John thinks about how there's less than two hours to go, then he can get back to Earth. He can't wait to dive back into that pool. It sure gets lonely up here, but it's not much longer now. However he realizes he's spoken to soon when he hears a distress call coming through. It's the Thompson Tower controller, who explains what's happened. They need help bad, and his buddy here said International Rescue were the people to contact.

As the fire continues to spread throughout the tower, the flames reach the top of the building. John contacts Tracy Island, and says the new Thompson Tower is on fire, and 3 people are trapped beneath it. Meanwhile the assistant confirms another section has been evacuated. The controller wonders how those people are doing in that corridor, as that's the last place he'd want to be trapped in a fire.

Blanche thinks nobody must know they're down here. Joe passes his son a handkerchief and tells him to breathe through it, as it'll stop some of the smoke. Joe asks why someone doesn't come, as they can't just be left to die down here. Jeff tells Scott to get over there straight away, as he won't get all the details until he investigates. Jeff then contacts the Thompson Tower staff, and says they've received their call for help. He wants all the information they have, so the controller starts to explain the situation.

Scott boards Thunderbird 1, and takes off. Jeff tells the control staff that Thunderbird 1 will be with them soon, and then tells Virgil to launch Thunderbird 2, and take the Mole with him. A little later, Virgil takes off in Thunderbird 2.

The assistant confirms that the entire building will be clear in 5 minutes. The controller says that'll only just be enough time, as the tower can't last much longer. He then questions how the corridor roofs will stand up to that heap of burning rubble. Blanche says she can't hold out much longer, and asks her husband why nobody is coming.

Joe asks who will come -no one can get them out of this now, and the whole Thompson Tower must be ablaze! Scott says he's approaching the danger zone, and Jeff says Virgil is 9.5 minutes behind him. Scott contacts the control center and says he'll be coming in to land. He then contacts Virgil and says he's over the tower now, and it doesn't look good. He asks him if he can cut down on his arrival time, and Virgil says he's not sure, it'll depend on wind variation.

Scott lands Thunderbird 1. The assistant says the entire building has been evacuated, but the controller says Thompson Tower has started to break up. He orders for the fire tenders to get clear, otherwise they're going to get buried. The assistant contacts the fire chief and tells him to clear the area. The fire tenders drive away from the tower.

Scott goes to the control center and takes a look at a map. He says they'll have to enter the corridors at a point which is half a mile away from D-50. The tower then comes down, and collapses. Joe says it sounds like the whole world is caving in. Blanche says it's gotten much hotter, so what are they going to do? Joe says to keep calm and hold on.

Virgil says he'll be there in 5 minutes. Scott tells him that the tower is down, so it's sure going to make their job tougher. He says that by the looks of things, they're going to have to cut through a whole heap of steel doors. He thinks Brain's gas is their only hope, there's no time to use something like a laser beam. Virgil says the gas isn't safe, prolonged exposure to it may be fatal. Scott says 3 people are going to die if they don't chance it, so what does he say? Virgil says the equipment is onboard, Brains had put it into the pod after the test. He tells Scott he's game, as if lives depend upon it, they must risk it.

Scott reports in and says what the plan is. Jeff asks him if he's certain there's no other way, and Scott says he is. Brains says he doesn't like this, as the gas masks are useless. Scott says the alternative is simple: they either chance the gas, or they take off and return to base. Jeff says he's right, and tells him to use the oxyhydnite equipment. Tin-Tin thinks that perhaps small doses of the gas will be harmless. Jeff thinks they'll be no time for an on off operation, it's all or nothing.

Thunderbird 2 lands. Scott tells Virgil they'll have to drill down to the corridor system in the Mole, that's the closest they can get to the folks in C-17. But first, they'll have to clear a sector of the burning rubble. There's a lot of soft rock there, so Scott tells Virgil to get the Firefly out of the pod and start clearing. But he needs to go carefully, as that rubble is white hot.

D-50's ceiling starts to crumble. Joe says this place is going to collapse soon. Blanche tells him to tell her they aren't going to die, and he says not to say things like that in front of their son. They've got to be brave, and he tells her to try and breathe gently, make use of every bit of air they've got left. But Tommy then collapses.

The doors to Thunderbird 2's pod open, as Virgil drives the Firefly out of it. Scott says he's heading over now, and is given a car to use. Virgil thinks the heat from the rubble is fantastic, so Scott asks him if the Firefly can withstand it. Virgil says they'll soon find out, and starts to drive the Firefly forward. It starts to shove the rubble out of the way.

The control staff wonder what the heck the Firefly is, and see that it's clearing the rubble easily. Virgil continues to drive the Firefly forward, but then it starts skidding. Scott asks Virgil how it's going, and Virgil says not so well. This rubble is getting difficult to dislodge.

He says that he's going to have to use the cannon. He takes aim at a large pile of rubble and fires several shots, causing it to break up. He then resumes driving forward, and now the Firefly can resume pushing it out of the way.

Scott arrives at Thunderbird 2, and drives the Mole out from the pod. Virgil finishes clearing enough rubble out of the way, and drives the Firefly back towards Thunderbird 2. He stops once he gets by the Mole, and boards it. Scott says to proceed to the drilling position.

The Mole makes its way through the cleared rubble, and reaches the drilling position. Scott says that from here, they'll be able to move down through the earth, and enter the corridor from the side. Virgil says here they go, as the Mole moves downwards and starts to drill into the earth. Scott says they know the family is in D-50, and the nearest corridor they can get through is C-17. All electronic systems have failed, so they'll have to cut through the steel fire doors. Virgil thinks that means they'll be working in the dark, but Scott says the emergency power plant for the lights is in the control center, which is their one blessing.

The Mole breaks through into the corridor. Scott and Virgil get the gear, and then ride on hover bikes to get to the first door. Virgil says that these doors aren't as thick as the test door, so they may be lucky. Scott agrees, but says there are more of these doors for them to get through.

Joe guesses that this is the finish. Scott starts cutting through the door, and tells Virgil to increase pressure to the cutters, as they aren't going to make it if they don't work faster. Virgil asks Scott how he feels, and he says he's fine, although that doesn't mean a thing.

The first door is cut, so Scott kicks it down. He and Virgil then get on their hover bikes and continue on to the next door. Scott starts cutting again, and asks Virgil if he feels any effects. Virgil says no, but it sure is hot down here. Scott gets through the second door, and kicks it down.

They get back on their hover bikes and go to the next door. Joe is banging on the door again, yelling for help, but then sees a fiery mark in front of him, which starts to get larger. He thinks this is it, the fire has reached them, so they're finished. But he then realizes that someone is cutting through the door -they're saved!

Virgil says this is the last door, and they've made it ok. Scott doesn't know how this has happened, and hopes Brains can supply the answer. He cuts through the door and kicks it down, where they see Joe. He says that his wife and kid are unconscious. Scott says they'll get them out of here.

Virgil says the roof is starting to cave in, so he and Scott get Blanche and Tommy on their hover bikes and leave. Moments later, the roof to the corridor does collapses, and the entire room is destroyed. Outside, the control staff see a large explosion, and realize that the ground has given way. The corridors have caved in, and the controller thinks whilst International Rescue tried, this was impossible. They died helping others.

The assistant then says to look over there, as they see the Mole reappear. The controller uses a radio and asks if anyone can hear him, and he hears Scott's voice. Scott says that they're all present and correct -they made it just in time. The controller thinks International Rescue is quite the organization -no one knows where they come from, but thank heavens they come.

Later on, at Tracy Island, Brains says that Scott and Virgil were saved by the heat in those corridors. He thinks it must be a characteristic of the gas, and explains that normally the vapor filters into the body via the pores, and attacks the blood cells. But when the temperature is high enough, it causes the gas to evaporate. All they have to do in future is use electrically heated gas cylinders. Scott thinks that's great, the equipment can be introduced as standard gear in all the Thunderbirds. Virgil asks Tin-Tin what she's reading. She reads out a news report about the fire, stating that Blanche and Tommy Carter were at an enquiry about the Thompson Tower disaster, and they all looked fit and well. The fire was started when a car crashed in the parking area, and the paper thanks International Rescue for their invaluable help. Jeff thinks that kind of makes the job worthwhile.

Scott wants to know something: Tin-Tin didn't mention if the driver of that car was male or female. Tin-Tin was afraid he'd ask that, and they've guessed it -the driver was female. Meanwhile, the driver from earlier is back on the road, and nearly gets into another accident. She thinks people like that are a menace. Her husband tells her she's so right.