Parker is reading a newspaper when he hears a car pull up outside. He thinks a butler's work is never done, but oh well... he'll have to finish reading about the "Killer of Clapham" some other time. He goes to the front door and meets Warren Grafton. Grafton says he has an appointment with Lady Penelope. Parker asks him to come in.

He tells Grafton that Penelope has been delayed, and asks him to wait in the library. Grafton asks if anything is wrong, but Parker says Penelope shouldn't keep him waiting for long. Grafton says from what he's heard, she's certainly worth waiting for. As he goes into the library, Parker uses a radio hidden in a statue to contact Penelope.

Penelope is driving FAB 1. Parker explains that Grafton is here to see her. She says she is running a little late, as she's being tailed. It may take some time to lose them, so she asks Parker to make some excuses to Grafton. Penelope decides to make sure the men following her are who she thinks they are, as she doesn't want to cause a scene unnecessarily. She allows the car behind her to catch up.

The other car has two men in it, and one of them reveals he has a gun. Penelope increases speed, as the guy with the gun starts firing. She thinks there's no doubt they mean business, so she must try to lose them. She deploys a smokescreen from FAB 1, but the other car drives right through it. Penelope realizes the car must be fitted with radar-assisted steering.

She decides to try something else, so she has oil leak out of FAB 1. The other car starts to lose control, but eventually the driver manages to stop it from going off the road. Penelope thinks that their car must have retractable studs in its tires, like FAB 1. She had hoped she wouldn't have to go to the ultimate lengths.

One of the gangsters starts firing a submachine gun, and Penelope thinks she has been left with no choice. She returns fire via FAB 1's own guns, which hit the other car and make it explode. It crashes off the road and is destroyed. Penelope tells Parker her mission has been successfully completed, and she's on her way home.

Parker tells Grafton that Penelope will be here any minute now. Grafton says to tell her not to rush, as he has plenty of time. As Parker leaves, Grafton takes out his lighter and pulls out an aerial on it. It starts making a humming noise, as he starts looking around the room. He can't find anything on the walls, but when he points the lighter towards the floor, it starts beeping. What he's looking for is under the floor, but he then wants to check the alarm systems.

He finds a wire behind a curtain. He thinks this is no problem, and places another device next to the wire. Just then, Penelope returns, and says she's sorry to have kept him waiting -she hopes he hasn't been too bored.

Grafton says on the contrary, as this room has proved to be most interesting. Penelope knows he's here about wanting some money, and asks what sort of charity does he run? Grafton says it's no charity, it's a business. He's the head of a syndicate concerned with the building and running of the Pacific Atlantic Monorail Company. They have 500 miles of track already built, and the most fantastic monotrain ever designed. Penelope asks what's so special about this monotrain.

Grafton says it's completely automatic. Penelope asks how much money he needs, and he says forty million dollars. But she's only one of the people they're approaching, they aren't expecting that kind of dough to come from one person. Penelope asks what's in it for an investor, and Grafton says a straight cut in the profits. If she buys shares, she gets a dividend, and the profits are going to be high! Penelope says he seems confident, but reveals she doesn't have a lot of money herself. Grafton says maybe not, but the pictures in this room along would fetch a few million. And then there's her jewel collection, that's internationally famous.

Parker then arrives with some tea, and also says a telegram has just arrived for her. As Penelope reads it, she sees it's from Parker, and it says that Grafton's chauffeur is a crook. Parker asks Penelope if it's bad news, but she says the news is a little disturbing. As Parker leaves, Penelope asks Grafton to continue.

Grafton says the scheme can't miss, this is a chance of a lifetime! Penelope says she never finances business ventures, as she's a mere woman who doesn't know enough about these things. But she has a very good friend who might be interested. Grafton asks if she thinks this friend of hers will help, and she says it's possible. He's extremely interested in scientific development, and is very wealthy. She'll see that he contacts him, and then asks him if his chauffeur would like a cup of tea. Outside, Grafton's chauffeur, Harry Malloy, is taking pictures.

As Grafton leaves, he thanks her, and says he sure enjoyed visiting her. He looks forward to hearing from her friend, and says so long. He returns to his car, and as he and Malloy leave, Malloy asks if she bit. Grafton says not exactly, but she's going to put some millionaire in touch with them. Malloy says they came here to get dough out of her, and Grafton says they will. He's fixed the alarm to stop operating just when they want, and he knows exactly where the safe is. She'll pay up, whether she likes it or not.

Parker says he'd know Malloy's face anywhere. That guy used to drive for an American mob that came over and tried to queer their pitch. Penelope thinks that's fascinating, and what an adventurous life he's led. Parker thinks this Grafton geezer must be a bit shady too. Penelope thinks he could be right, as this monorail project sounds a bit too good to be true. She decides to contact Jeff Tracy, as he'll know what to do.

At Tracy Island, Penelope's picture starts flashing. Jeff asks what's up. Penelope says she's onto something that needs investigation. Jeff says if it's something that anticipates a disaster and saves them a rescue operation in the future, they're all ears. Penelope explains about Grafton's visit, and what he wanted.

Alan recognizes the name immediately, and says it must be the Grafton of Pacific Atlantic. Scott says that company has been having trouble with the US government about safety precautions. Penelope says she told Grafton she had a friend who'd be interested. Jeff says that must mean him, and he's always on the lookout for interesting engineering investments. He asks where he can get in touch with him, and she says Grafton will be returning to his New York office tomorrow.

In New York, Grafton is telling his underlings that the Pacific Atlantic Monorail Corporation is really going to be in business. He asks his men how their ventures are going, and finds out that they're set to make a killing at Monte Carlo. They should be able to clear four million bucks at the casino. And an oil deal in South America will net them seven million without the authorities getting near them. Another racetrack venture will get them ten million. Grafton says that's 21 million dollars, so just 19 to go. He tells everyone he has just organized the greatest combined operation in the history of big business. Tomorrow night, Malloy and Selsden will gain entry to the mansion of Lady Penelope Creighton-Ward in England, and walk out with one of the world's richest jewel collections! At the same time, here in the States, he shall be taking Jeff Tracy and his two advisors for a trip on the monotrain.

The next day, Jeff's group are on the monotrain with Grafton. Grafton asks Jeff what he thinks of it. Jeff thinks this coach certainly is comfortable, but wants to know what the government hasn't backed him. Grafton says he never asked them, as he wants guys like Jeff to benefit. Private enterprise is what keeps this country on its feet. Brains thinks the monotrain is a superb piece of engineering skill, he just hopes it has been thoroughly tested.

Grafton says sure it has, some of the biggest men in the country are behind this project. Jeff asks what sort of men are they? Grafton says he must understand, they're modest men, men like him who try to stay out of the limelight, so they can get the job done without a lot of ballyhoo. Jeff wants to know a lot more about the system, and the people behind it. Brains says he believes the train is automatically controlled. Grafton says the whole track, from beginning to end, is controlled by automatic signals. Jeff asks if there is a safety risk, but Grafton scoffs at the idea of risk, and says crossing the road is taking a risk. Jeff says maybe, but that's not the attitude to take when people's lives are involved. Grafton says a fleet of helijets is on constant patrol, if anything is wrong they'd report it immediately.

Helijet 304 pilot Joe is flying over a section of the monorail. He tells base that he has nothing to report. Base says that's swell, as nothing must go wrong. Joe says the monotrain should be on its way, but then hears a loud noise. He says they're in for some rough weather, as a storm starts overhead. It starts raining, but there is also lightning.

Joe tells base this is useless, and says he's going to shut down for a spell. As he starts to move away from the storm, a bolt of lightning hits his helijet, causing it to go into a dive. Joe has no choice but to eject.

His helijet smashes into a bridge, which has part of the monorail track on it. The helijet explodes upon crashing. As Joe parachutes down, he sees that some of the automatic signals are on fire.

He parachute snags on part of the bridge, but he says he's got to contact base and stop the train. The bridge has been badly damaged, and continues to deteriorate. Joe reports to base that he's crashed, and the monorail is going to collapse. He says that the train has got to be stopped.

Grafton says that in the standard coaches they can pack in 500 people. Jeff thinks "pack in" is right, and says so far he's not overly impressed. Grafton says if he wants to be impressed, he should come up front and see the power unit, as that'll impress him. Meanwhile Joe is still trying to contact base, stating that it's an emergency.

Grafton shows everyone the power unit, which he says is the greatest chunk of engineering genius in land travel history. Brains asks if he and Tin-Tin can examine it, and Grafton tells them to help themselves. But he warns them that it has taken some of the best brains in the country to put that box of tricks together. He tells Jeff he's not begging him, but he thinks he'd be a fool not to swing in with them. Jeff says he doesn't know, as people aren't cattle. Grafton says that's where he's wrong. There's a few of them who lead, and the rest follow like sheep.

Brains asks if everything is completely automatic -the train carries no staff at all? Grafton says he doesn't need staff, and think of the money they're going to save. Brains asks about what would happen in an emergency, but Grafton thinks he worries too much. Meanwhile, the damaged bridge continues to explode in places.

Another helijet piloted be a guy called Stan turns up at the bridge. Stan lands his helijet and goes onto the bridge. He tells Joe to keep still, he'll winch him up in his helijet. But Joe tells him to radio the train first, and tell them that the automatic signals are all out of action. He's tried radioing base but his transmitter must have been smashed. Stan heads back to his helijet.

The monotrain continues on the track. Grafton says that nothing can go wrong with the signals. Jeff asks how he can be certain, but Grafton says they've spent enough money on safety devices. He starts saying there is an element of risk involved, but then a buzzer goes off. He says that's the radio and excuses himself, saying he'll be right back.

Jeff asks Brains what he thinks. Brains says he's not too happy, as there are too many loopholes. Jeff thinks he's right, and Grafton is more interested in money than in people's lives. His type usually end up in once place: jail. Meanwhile, in England, Selsden tells Malloy that they'll end up in jail if they're caught. Malloy says they've taken worse risks than this, and Grafton has fixed the alarms. All they've got to to is press a button and they're ok.

They arrive at Penelope's mansion, and park their car on the drive. Penelope and Parker are sleeping, so the two head up to the front door. Selsden starts to pick the lock, and says it's tricky. But they should manage it ok. Malloy hopes that Grafton is having it as easy as they are.

Grafton goes back to the group and says something has gone wrong, and they're heading for trouble. At the bridge, Stan brings his helijet over to where Joe is and winches him up. Stan says this whole section is going to collapse at any minute. Joe wonders if there's any hope for them, but Stan says if the signals are out, then the train can't stop as it has no manual control.

In the monotrain, the group have gone back to the power unit. Jeff asks Brains if he can stop this thing, but Brains says he doesn't see how without a circuit diagram. Tin-Tin says that even with one it wouldn't be certain they could succeed. She asks how long they have, but Grafton has started panicking and says they're increasing speed all the time. Jeff tells him that's obvious, and asks when will they come to the damaged part of the track? Grafton says he doesn't know. Jeff thinks he's a great help.

At the mansion, Malloy and Selsden have gotten inside. Malloy says those alarms have been knocked out good, so the two enter the library. Selsden says Grafton had mentioned there being closed-circuit TV cameras in all the rooms, but Malloy says Grafton's alarm system jammer took care of those too. They're in the clear, so he needs to relax. They go further into the room and find the place where the safe is. They pull up the rug and see the safe door, but Selsden says it'll take some time to open it. Malloy tells him to quite stalling and get on with it.

Back at the bridge, Stan and Joe watch as another explosion causes part of it to fall away at one end. Stan thinks that does it, nothing can save that train now. In the train, Grafton demands the train is stopped, as what's going to happen to them? Jeff thinks he should have thought about that before, but for now he needs to keep calm.

Jeff whispers that he's going to call the boys, but Brains says it's too late. Jeff has realized that, but if he fails then they might need help after the crash. Brains asks how he can call them without Grafton finding out they're from International Rescue. Jeff asks Grafton if he's heard of International Rescue. Grafton says sure he has, but no one knows who runs the outfit, or where they come from. Jeff says he can't say, but he believes to call them you just have to send out a radio message. Grafton and Jeff leave the room to make the call.

Brains tells Tin-Tin here goes. He pushes a button, but the train does not stop, and Tin-Tin realizes that they're increasing in speed! Meanwhile, Jeff makes the call to International Rescue.

John picks it up, and realizes it's his father. Jeff tells him this is urgent, as the monotrain is out of control and they are headed for a damaged section of the track. He tells him how many of them there are on the train, so John says that International Rescue are on the way. He then contacts Tracy Island, and explains to Scott and Virgil what's going on.

Virgil thinks they'll never get there in time. Scott thinks that may be, but they can't just sit here. He goes to Thunderbird 1 and takes off, whilst Virgil takes off in Thunderbird 2. Back in the train, Brains tells everyone to keep their fingers crossed as he tries pressing the button a second time. But it still doesn't work, and the train keeps going.

Back at the mansion, Selsden says another minute and he'll have it. He manages to unlock the safe, but as soon as he does, it sets off another alarm in Penelope and Parker's bedrooms. Malloy opens up the safe door, and tells Selsden to take a look at that: Penelope's fabulous collection of jewels.

Penelope can see via a hidden camera that two men have opened up the safe. She contacts Parker via radio and says it appears they have visitors. Parker can see the two guys as well, and says it's their old friend Malloy. Penelope says they must stop them before it's too late, but Parker thinks it may be too late already, as they've probably got a car standing by. Penelope thinks they have no choice, and Parker says he was thinking the same thing. He says he'll get the hardware.

Malloy and Selsden have taken everything, so they decide to beat it. They get to their car, but before they can start it up, they get shot at by Penelope and Parker! Selsden asks who the Calamity Jane is. Malloy tells him that's the duchess, and then tells him to come on. The two make a break for it towards some trees.

Parker shoots out some of the tires on the car. Malloy says the car is knocked out, and Selsden asks what are they going to do? Malloy spots a garage nearby, and thinks there is bound to be an automobile in there.

Parker says the guys are heading for FAB 1. Penelope thinks that won't do them much good. Parker is trying to comprehend how these guys got in, as he didn't hear any alarms. Penelope thinks they must have put them out of action somehow, but luckily for them the safe alarm camera operates on a different system. They then hear some glass smashing, and Parker says it appears they've gained access to the Rolls Royce. Penelope hopes they don't scratch the paintwork, as she's off to Ascot in the morning.

Malloy drives FAB 1 straight through the garage door, knocking it down. Penelope doesn't want Parker shooting up the Rolls Royce, so she instead turns one of her bed's banisters. Malloy suddenly finds that the car is just going in circles, and he thinks this is Penelope's doing -she must have this car under remote control, and she's locked the wheel!

Penelope says they can go back to bed now. Parker asks about their visitors, but Penelope says they can forget all about them until the morning, as they'll still be around. Meanwhile, FAB 1 continues to drive in circles around a statue.

Joe says the other end of the bridge is giving way, and Joe thinks the whole thing will collapse soon. They then see the monotrain on the horizon, so Joe says they'd better radio for emergency services. In the train, Grafton says they're approaching a bend, they've got to stop this thing!

Brains says this is their last chance. He presses the button again, and this time, the monotrain's brakes activate. As the train begins to slow down, the brakes spit flames on the track. Jeff thinks Brains has done it, but Brains hopes there's enough track left. Grafton screams that they are still going too fast. Jeff tells him to shut up.

The monotrain stops just before the gap in the bridge. Stan reports to base that the train is ok. They've called for the emergency services, and are now returning to base. His helijet's endurance is down to five minutes. He ends the call and then he and Joe head back to base.

Scott then arrives in Thunderbird 1. He asks Virgil what his estimated time of arrival to the danger zone will be, and finds out he's six minutes away. Scott says he's above the monorail now, and it looks like the train made it. Everyone in the train sees Thunderbird 1, and Jeff guesses this must be the International Rescue guys. Scott tells them they're still in danger, as the tower behind them is going to collapse at any moment.

Parts of the bridge continue to explode and fall away. Scott says he's going to try and push them back off the trestle, but as he approaches in Thunderbird 1, the bridge's status gets even worse. He realizes the rear part of the trestle can't stand the train's weight. He tells everyone to hurry through to the rear of the train, and then walk back down the track. The group get to the back and open up a door, which has a ladder drop down.

Grafton looks outside, only to see another part of the bridge collapse, making it impossible for them to walk along it. He asks what are they going to do, as there is no way down! Jeff says for a start, they'll keep calm. Scott tells everyone to go back to the center of the train, as Thunderbird 2 will be here any moment. Thunderbird 2 then arrives, and heads towards the monotrain.

Virgil lowers grabs from Thunderbird 2, which drop down. They surround the carriage everyone is in, but the bridge then shakes, as more pieces of it fall apart. Everyone inside the carriage gets knocked over, as Grafton asks what's going on -are they trying to murder them or something?!

There is another explosion at the back of the bridge. Scott is watching and tells Virgil to close the grabs, so he does so. Virgil then makes Thunderbird 2 ascend higher into the air, pulling the carriage along with it and breaking it away from the rest of the monotrain. This happens just in time, as what's left of the bridge finally gives away. It and the rest of the monotrain plummet.

Virgil moves Thunderbird 2 over to a cliff edge, and he places the removed carriage down on the ground. He tells Scott to leave everything to him now, so Scott says he's returning to base. Thunderbird 1 then moves off.

Grafton says they made it. Jeff guesses he won't be needing his investment now, as after the government enquiry into this crash he'll be spending a nice, long holiday behind bars. Grafton tells him that's where he's wrong. He believes he's too smart, and he'll get away with the inquiry. He'll end up being the president of the greatest monorail network in the world!

Sometime later, Grafton is in jail, pretending to give a speech about his company. The rest of his gang are also in jail, and tell him to cut it out. Selsden says he's still giddy from that society dame's crazy pink drag! Malloy says she kept them turning all night, he was even glad to see the cops the next morning. Grafton says all they need is a little more dough, but everyone thinks he's wasting his time. Grafton says time is one thing they've got plenty of.