Alan and Grandma Tracy are on the San Miguel bridge. They have been left there by two men, who drive away in a red car.

Alan tells Grandma that whatever she does, she must not move. She says she doesn't understand what that little object there can do. Alan says to save it, as the slightest move from either of them will detonate the bomb under that's under the bridge. Under the bridge, a small bomb has been planted.

Alan says it's coming up to noon. Grandma says it sure is hot, but then notices Alan moving. He slowly moves his arm up, and says he's just trying to reach his telecom. Grandma says to remember what they were told: if they disturb the ultrasonic waves, that thing could blow them sky high. Alan makes a call to International Rescue.

Alan gets straight through to Jeff. He tells his father they're in serious trouble, as they're on a bridge and can't move. Jeff summons Scott and Virgil, as Alan explains the situation. He hopes they can get here before they pass out from the heat. Jeff says Scott and Virgil are on the way, and they'll get to them in time. He tells Scott and Virgil to launch Thunderbirds 1 and 2, using pod 1. He'll give them their course and full details when they're airborne, but if they want to save their brother's life, move! Jeff then tells Brains to get down to Thunderbird 2 immediately.

Scott and Virgil get to their Thunderbirds, and take off. Back at the base, Jeff and Tin-Tin look at a map, and find the San Miguel bridge. Tin-Tin says that's a lonely spot, and Jeff says the bridge won't be open to the public for two months yet. Whoever did this certainly knew what they were doing when they planned it. Tin-Tin asks when the bomb is due to go off.

Jeff says sometime around 1300 hours, according to Alan. But that's only part of it, as there's a ultrasonic generator there which can detonate the bomb earlier if anything on the bridge moves. He tells her to pass this information on to Scott and Virgil, whilst he works out a plan of action. He hopes Alan and Grandma can hold out, but the noonday sun can be pretty savage in those parts. At the bridge, Alan says International Rescue must be well on their way by now. But Grandma doesn't think she can take much more of this heat.

She then passes out, but remains upright. Scott reports to Jeff that he's proceeding to the rescue zone as according to plan. He asks how Alan and Grandma are, and Jeff says he'll contact them to find out. Alan says that Grandma has passed out, but she'll be ok as she can't fall. It's himself who's likely to spoil the show, as he just has to relax for a moment, and down he goes. Jeff tells him he's got to stay with it, and not let himself go. Alan says he can't seem to concentrate.

Tin-Tin tells him to listen to his father -whatever happens, he must not break his concentration. Jeff tells him to concentrate on what he's got to say. He tells Alan to keep talking until Scott and Virgil get there.

He wants to know exactly how Alan got into this fix, starting from the beginning and telling him the whole story. Alan says ok, and says it all started the day they went to Parola Sands. Everything was going the way they'd planned, and it looked like nothing could go wrong. From up there in Thunderbird 2, the world sure looked pretty...

Virgil says they're nearly there. Tin-Tin tells Alan she's found it, and says when he reaches the highway and turns left, he'll come to the racetrack on his right. Alan says that's where he'll meet Kenny Malone, a great mechanic. He can't wait to show him what they've got in the pod, and thinks it's a pity Virgil and Tin-Tin can't come with him. Virgil says he knows they can't, as supposing what would happen if their father received a distress call whilst they're gone? They'll be watching the telecast instead. Alan guesses he's lucky to get leave like this. Tin-Tin says this isn't just a pleasure trip, as Brains will want to know how his new engine works under prolonged stress.

Thunderbird 2 lands, and rises up. Tin-Tin tells Alan to not forget that they'll all be watching him, and she wants him to give her love to Grandma. Alan says he will do, as the pod door opens up. Alan drives out his new car, and heads away from Thunderbird 2.

Alan receives a call from Virgil. Virgil asks what the first impressions are. Alan says the car is great, and to tell Brains he's done it again. Virgil tells him to take it easy, as he doesn't want to get a ticket for speeding. Alan says he can't wait to try the car out tomorrow at the Sands. Virgil tells Tin-Tin their mission is completed, so they'd better get back to base. Tin-Tin wishes she was going with Alan, to keep him company, you know? Virgil says he knows. Thunderbird 2 then takes off.

Alan arrives at the Parola Sands racetrack. He heads into the automobile park, which features a stacking system. As Alan stops at the bottom, a guy controlling the stacker picks his car up, and lifts it high into the car park. As Alan gets out of the car, he hears someone over the intercom paging him, telling him to go to the cocktail bar in the main building.

In the bar, Alan meets up with Kenny. Kenny thinks Alan must miss the excitement of the circuit, and asks what he's been doing with himself. Alan says this and that -family business. He then sees someone nearby he recognizes: Victor Gomez. Gomez asks Alan when he got into town. Alan says he just got here, but Gomez says he thought Alan had retired from the racing business. Alan says you won't get rid of him that easily. Gomez has heard Alan has brought quite a car, does he reckon he's going to win the trophy? Alan says he'll let him know, and then he and Kenny walk off.

Johnny Gillespie tells Gomez he thought he'd said Alan Tracy had quit. Gomez says it looks like Tracy changed his mind. Johnny says he doesn't like this, as they had this contest all sewn up until that guy came along. Nothing has got to stop them from getting that prize money. Gomez tells him not to worry -nothing will. The next day, the race is in progress, as Alan takes the lead. Gomez is in second place, whilst another racer called Webster is in third.

The commentator says that history is being made here, as it seems nothing is impossible for the machine and its driver, Alan Tracy. But the genius who invented it still prefers to remain anonymous. As Alan and Gomez turn round a corner, Webster loses control, and crashes. The commentator says that one year ago, America's most promising racing driver, Alan Tracy, announced that he was retiring from the racing world. But now, he's sweeping round the course, heading for what seems to be certain victory.

At Tracy Island, everyone is watching the race. The commentator says these two cars are fighting it out over the last few miles of the Parola Sands circuit. Gomez manages to pull alongside Alan, but Alan manages to stay ahead. The commentator says what a finish this is going to be! Tracy and Gomez are now neck and neck as they battle their way to the finish. Gomez is making a desperate bid to get the better of Alan Tracy. He says that the two cars are moving out of sight as they come into the difficult cliff stretch.

As the racers get to the cliffs, Alan remains in the lead. But Gomez is then able to catch up, and moves right next to Alan's car. He starts bumping into Alan, but is unable to push him out of the way, or get ahead. The two cars get around another turn, and whilst Alan's car breaks through a barrier, it remains on the road.

Alan races over the finish line, and wins the race. The commentator says that the winner in today's exciting competition was Alan Tracy, who gained a lead over the former champion, Victor Gomez, in the last lap. Gomez tells Johnny they should have fixed Tracy's engine like he'd suggested. Johnny wants to get his hands on the design for that car, but now he has a plan to fix this Alan Tracy for good. At the island, everyone sees Alan receive a trophy for winning the race.

Back in the present, Alan says that was some victory, and now this. Jeff contacts Scott and tells him to keep up maximum speed, as Alan is in a bad way. Jeff then tells Alan he's doing great, and tells him to go on with his story. Tin-Tin notices that Alan isn't responding.

Jeff tells Alan to listen to him: he's got to keep on talking. Scott and the others are well on their way now, so he needs to keep it up. He asks Alan what happened after the race. Alan says he remembers, he and Kenny took the car back to the stacker. Alan asks Kenny to stack the car for him, he needs to make a telecall. As Alan walks off, the car is stacked.

Kenny gets out and heads to the cocktail lounge. The guy operating the stacker then gets hit on the back of the head by a wrench. Johnny asks Gomez if he killed the guy, but Gomez says no -it was just a little tap to keep him out of the way for a bit. Now, they're going to fix Mr. clever guy Tracy.

They see Alan in a telecall booth. Alan is making a call to Grandma Tracy, who thinks it's thoughtful of him to call her so soon after the race. She was that excited! Johnny tells Gomez to hurry it up, as they don't want to get caught in here. Gomez says he hasn't got used to these controls yet.

Alan tells Grandma to get her bags packed, but she says she's packed already. She's dying to get a ride in that lovely car of his! Meanwhile, Gomez uses the stacker to start pushing a car off of its platform. But he and Johnny then see another car at the bottom of the car park, which starts using its horn. Johnny and Gomez decide to beat it.

Alan leaves the telecall booth, and seconds later the car comes crashing through it. Back in the present, Alan says that when the stacker attendant came to, he sounded the alarm, but it was too late to stop Gomez and Gillespie. Jeff tells Alan to keep going -what did he do after he left the race? Alan complains about the heat, and doesn't think he can say more.

Jeff asks him what did they do next, where did he go then? Alan says he set out to collect Grandma. At her home, Alan has just had some apple pie, and thinks Grandma's cooking is certainly going to be popular at the base. Grandma can't believe she's joining the International Rescue team at last. She's proud of all the things they do, but she's a celebrity around these parts too.

She explains that after Alan won the Parola Sands competition, she had the press round asking her questions. Alan asks her what the press wanted, and she says they asked about who designed the car, and what route they would be taking for their trip together. Alan hopes she didn't tell them, and she says she told them alright -she told them everything they already knew. Jeff contacts the island, and says they'll be leaving in a few minutes. He and Grandma then head out in the car. Grandma thinks it's lonesome out here, but Alan says it means they can travel faster.

But they see Gomez waiting on the road, who has a gun. Grandma recognizes him, and tells Alan he was one of those so-called reporters who interviewed her. Alan asks Gomez what he wants. He asks what sort of a tone is that to talk to a guy with a gun in his hand? Alan says if he wants the award money, he's wasting his time. It has already been given to the Parola Sands charity fund. Gomez says it's not that, but once Alan is out of the way, they'll be plenty of money for them again. Johnny then appears, and says they don't want to waste any more time on Alan. He's put the road signs back the way they were, so they aren't going to be disturbed.

Johnny gets in the car. Gomez tells Alan to drive the car round the corner, and stop at the center of the bridge. Johnny says no more tricks, as he has a gun pointing at the old lady's head. He tells Alan to get going, so Alan starts the car up and drives away. They soon arrive at the bridge, and come to a stop on it.

Back in the present, Jeff tells Alan he's doing great, and he must not give up, not now. He wants to know what happened next, but Alan asks how the boys are doing, as he can't hold out much longer. Jeff says he'll put Scott through to him, so he can hear for himself. Scott tells Alan that they aren't far away, so he must keep his ears open for the sound of their jets. He's just crossed the Pacific Coast. Jeff asks Alan to carry on, once they were all at the bridge, what happened then? Alan says he remembers...

Alan says he doesn't have the plans for the BR2, and if he had, did they think he'd hand them over? Gomez tells him if that's the way he wants to play it, he and the old lady can get moving. Alan says that this has nothing to do with Grandma, but Johnny tells him to cut out the hearts and flowers. He passes Alan a device, and tells him to take it with him. He then orders Alan and Grandma to climb the ladder. He thinks Alan and his buddies are on to something new, and they want to know what it is. They were the tops, until Alan whipped them. Alan and Grandma get onto the bridge. Johnny orders Alan to put that generator down in front of him. As Alan does so, he tells Grandma to sit down next to the support.

It is revealed that there is a bomb under the bridge, which is going to go off in a couple of hours. But Gomez says that generator is an extra present. They're going to leave the bridge, but if either of them make just one move and disturb the ultrasonic waves from the generator, the bomb goes off ahead of schedule. They're going to switch is on by remote control. He then removes the ladder, and gets into the car with Johnny. They then drive off the bridge.

Back in the present, Jeff sends Brains a picture of the bridge that Tin-Tin had found. Brains thinks they at least know what sort of terrain they'll be working on. They can't go too near the bridge, as they don't know how localized that generator's power is. Jeff tells Alan it won't be long now, so he just needs to hold on. Scott should be with him any minute. Thunderbird 1 arrives near the bridge, and lands.

Scott tells his father he's landed, but this is going to be a tricky one. He asks Jeff to give Virgil some landing coordinates, whilst he contacts Alan. Scott tries to reach Alan, but Alan keeps saying he's got to keep awake. Scott thinks he's delirious, but tells him to raise his left arm and look at him. Alan eventually does so, and Scott asks him how localized are the ultrasonic waves from the generator. Alan says to keep away, and not come near, as it will detonate the bomb. Scott asks him if he knows how powerful the generator is.

Alan says he can't go on much longer, he can't feel his legs anymore. Jeff tells him two more minutes, as Virgil is nearly there. He wants Alan to remember the code of International Rescue: to not give up at any cost. Meanwhile, Virgil arrives near the bridge, and tells Scott he's coming in to land. Scott says to make it fast, as Alan's almost had it.

Thunderbird 2 lands, and raises up to reveal pod 1. Alan says he's going to fall, he can't take any more. Jeff tells him one minute more, as Brains is going to neutralize the generator. They don't have time to look for the bomb itself, but Jeff tells Alan to hold on, as he's going to be ok. Back at the pod, Brains rolls out in the neutralizer tractor.

He gets to a point where he can see the bridge, and uses a telescope on the tractor to locate the generator. He then activates the neutralizer, which starts to make a loud buzzing noise. After a few seconds the generator is heard crackling, and Brains reports that it has been neutralized. He gives Virgil the ok.

Virgil then rolls out of the pod in the jet-air transporter. He drives this onto the bridge, and gets to where Alan and Grandma are. He turns the machine on, just as Alan falls.

The machine hits Alan with powerful blasts of air, which stops him from hitting the ground. Virgil moves Alan and tells Grandma she's next, and they don't have much time. Grandma jumps down off the beam, and she is saved by the air blasts.

Virgil says they must clear the bridge, as it's going up at any moment. The group leave the bridge on the jet-air transporter, and clear it seconds before the bomb goes off. The explosion causes the bridge to break up, and it falls down into the canyon below.

Meanwhile, Gomez and Johnny are trying out the BR2. Johnny tells Gomez to keep on the road, but Gomez says he can't get used to this geared steering. They then hear something approaching from behind them, and see Thunderbird 1. Thunderbird 1 opens fire, hitting the ground next to the car. Gomez realizes Tracy and the old lady must have escaped! Johnny says they have to lose this guy.

Scott makes another pass, firing again. Gomez thinks they've got to stop, but Johnny leans over and tries to take control. Gomez tells him to let go, he's going to crash the car! Scott sees the car veering all over the road, and thinks they've gone crazy -they're going to crash!

The car ends up slamming through a barrier, and it tumbles down a cliff. Virgil contacts base, and says they're leaving the danger zone -mission successfully completed. Thunderbird 2 then takes off.

Sometime later at the island, Virgil is painting a picture of Alan. He tells Alan that whatever he does, he must not move. Alan is getting fed up, and asks how much longer will he be? He's tired of having to stand dead still like this. Virgil asks him how he's going to get a good likeness of him if he doesn't keep still. Tin-Tin thinks he should smile, as he can't go down in motor racing history with an expression like that. Alan says this trophy is darn heavy.

Scott comes over and thinks Virgil's work is great, he's really caught a likeness. Virgil says he's finished, and spins the painting around. He asks Alan what he thinks of it. Alan supposes they must think this is funny. Scott says not at all, and tells Virgil he thinks his work is very good. Alan agrees, except the technique is about 100 years out of date!

Virgil tells him he must admit it's really him, which Scott agrees with. Alan walks over to Jeff's desk, and tells them to laugh this one off. He presses a button on the desk...

...which causes Virgil and Scott to drop down. As they tell Alan to cut that out, Alan asks Tin-Tin about the painting. She tells him never mind, as who needs a painting? Especially when she has the real thing.