At London Airport, the emergency services are sent out. As Flight D103 makes its final approach, all the emergency vehicles are told to take up crash positions. The plane crew confirms that there has been a hydraulic failure in the undercart. Norman tells the pilot that the emergency crews are in position and offers him good luck. The pilot says they may need it. The plane crashes down on a runway.

As it slides to a stop, it explodes, just as the emergency vehicles get to it. It's revealed all of this was being played back on a screen. Captain Saville tells everyone in the room that what they've just seen illustrates the greatest danger in any crash landing: the tremendous fire. One reporter asks if an answer has been found with Skythrust. Saville says their extensive tests have shown Skythrust is the safest plane flying today. He tells everyone to go up to the roof to meet the designer and see Skythrust.

The designer is Brains, who is using the alias of Hiram K. Hackenbacker. He contacts Jeff Tracy via radio and tells him he's now entering London Airport. He then drives his car up to a security gate, and after checking his ID, the guard there lets him through. Brains soon joins everyone on the top of the building, where they wait to see the Skythrust.

Skythrust is soon raised up from an underground hangar, and waits on the runway. Whilst Saville congratulates him, Brains says he can't take full credit for it, he only designed some of its new, experimental features. Inside the Skythrust's cockpit, Captain Ashton reports they're ready to commence the test routine. Norman tells him to go ahead.

Skythrust takes off successfully. Saville says he just couldn't fault that take off. Brains says he's rather satisfied with Skythrust's behavior, though as far as he is concerned the full test of her abilities has yet to come. One reporter asks what he means, what's special about Skythrust that they haven't heard about? Norman says they can't answer that yet. Skythrust does incorporate certain new features, but they're not in a position to divulge these at present. The reporter asks when Skythrust is due to come into service. Norman says very soon indeed.

Brains says he's going to go up to the control tower to hear the latest with Ashton. At Tracy Island, Scott reads a report about Skythrust and its supposed revolutionary new features. The report also mentions Hackenbacker, the brilliant American designer and well-known man of mystery, who wouldn't give any information about the aircraft he played a large part in designing. Virgil asks if the article mentions when Skythrust is going to go into service. Jeff thinks it must be any day now, that's why Brains is staying on in Europe.

Scott reads out that very soon it's expected that the first flight will be London bound from Paris. Tin-Tin says speaking of Paris, and shows everyone that Penelope is on the front cover of the magazine she's reading. She reads out that excitement in the Paris fashion world mounted today, as Lady Penelope announced she might participate in a charity fashion show presented by Francois Lemaire. Francois Lemaire is her and Penelope's favorite fashion designer. She then reads that Lemaire has something really sensational to offer this year.

Penelope has gone to see Lemaire in Paris, as he invited her. He is happy that Penelope has decided to model for him at the premier. She asks him what wonderful surprises he has in store for them this season. Lemaire promises her that his creations will go down in history, they will be a sensation! He's about to say what his secret it, but Penelope tells him to wait.

She pulls out a hairbrush, but it has some kind of scanner in it. She says one can never be too careful, and starts using the scanner. She tells Lemaire that he's being bugged, someone has planted a transmitter in the room and can hear every word they say. She holds the scanner over some flowers and says she thinks she may have found their little secret. She pulls out a small transmitter from one of the flowers.

She then looks through a telescope and says very clever, but not quite clever enough. She closes the curtains and tells Lemaire that his office has been under constant surveillance by a long range television camera. Lemaire decides that, just in case it's not safe, he'll write his great secret down on paper. He goes over to his desk and starts writing a sentence.

But before he can finish writing, Penelope stops him. She asks to look at his pen, and when she opens it up, she asks how long he's had it for. Lemaire says he doesn't know, he hardly ever uses it. Penelope thinks that's good, it's probably note too late. She tells him to watch this, and writes out another sentence stating that it'll take better men to find out the secret.

Penelope says this is an impressor pen, which can record and transmit anything the writer commits to paper. It means that at this very moment the pen is sending a message to his enemies. She says she'll prove it, and pulls out a small black box. This box starts printing off the message that Penelope had just written down. Lemaire thinks this is too much, he needs reviving!

He asks Madeline to bring some tea in. He then asks Deirdre to standby to model the new items that arrived this morning. As he ends the call, he explains to Penelope that they are his two leading models. They are going to assist Penelope during the show, but she asks if they know his secret. Lemaire says they do, and shows Penelope what it is. He pulls out a small box.

He opens the box and pulls an entire dress out of it. He says it's his new fibre: Penelon, something he named after her. He says that Penelon can be made into any kind of costume desired. It never gets crushed and it can squeeze up into the smallest space. Penelope thinks she could carry a whole wardrobe around in her handbag. Lemaire says it can be made to look like any other material. He displays some images of his models in different outfits, such as one which looks like a leather outfit, but he explains it's made entirely of Penelon. Madeline then brings the tea in and asks if Penelope takes sugar.

Penelope looks at the bowl of sugar and sees one lump which is rather big. She puts it in her tea and watches it dissolve, revealing that it had another transmitter inside it! Lemaire says he's at the end of his wits, surrounded on all sides by enemies -what is he to do? Penelope says the arrangements for the preview must be changed. They dare not hold it in his salon, as the risk is too great. She thinks of a place where there'd be no danger of interruption, and thinks she knows just the place. She says she'll have to contact a friend.

At London Airport, Saville says Skythrust is ready to go into service immediately. Norman says the final tests have proved most satisfactory. A message then comes through stating there's a call for Mr. Hackenbacker, which he needs to take outside. Brains eventually remembers he's Mr. Hackenbacker, so he heads outside. He realizes Penelope is speaking to him, and she has a big favor to ask of him.

Penelope meets with Ashton at a restaurant. Ashton wants to know how she came to know Hackenbacker. Penelope tells him he must allow a lady a few secrets, but she will say that the two of them are associates. She asks about this scheme of hers, but Ashton thinks it's a lot of trouble to go to just for a fashion show. Penelope thinks that's just like a man, but then the waiter brings them their coffee. Penelope then gets a call from Parker, who is outside in FAB 1. He tells Penelope he's getting a reading, there is another one of those transmitters bugging them.

Penelope says it must be the coffee pot. She lifts the lid off of it and finds a transmitter attached on the other side. She looks over at where the waiter is, and he immediately runs off when he sees her. Ashton says he doesn't understand. Penelope says the waiter planted the transmitter to overhear their conversation. Ashton wants to get his hands on him, but Penelope says he'll never catch him now. And even if he did, the guy would tell them nothing. She asks Ashton if now he sees how important this fashion show is. Ashton says he does, so they must switch the location of the preview.

The new location is going to be on Skythrust, which rolls out onto a runway. Ashton tells Mason to open up the freight deck, but he presents him with some telegrams first. Ashton reads one from Hackenbacker, which says they'll be waiting with the champagne at the other end. The co-pilot just wishes Hackenbacker could have come with them on their first commercial flight. Ashton says never mind, as this flight is going to be special enough. He tells Mason to get the freight deck loaded. Outside, Lemaire, Madeline and Deirdre head towards Skythrust via car. Lemaire says he gets butterflies every time before a new collection is shown, but this time it feels like a herd of buffalo! Madeline tells him to relax, as when this collection is shown to the buyers, he'll be the toast of the fashion world. Lemaire thinks sometimes her calmness borders on cold bloodedness.

He asks Deirdre if the costumes are still alright, and she says they are. They're all in small boxes right next to her. Madeline drives their car into the Skythrust. Meanwhile, Penelope and Parker arrive at the airport in FAB 1. Parker drops off Penelope and then leaves the Skythrust.

Penelope asks Lemaire if everything is ready, as they must not keep the buyers waiting. Lemaire says that the airline people have done a beautiful conversion job. He takes Penelope through to the next room, showing her where the fashion show will take place. Penelope thinks it's charming. With everyone now onboard, the Skythrust takes off.

Lemaire tells Penelope to go and get changed as soon as they've leveled out. Penelope tells him not to worry, they shan't let him down. Lemaire then asks about the music. Deirdre says that Mason is taking care of that, and whilst he's new to the airline, she's explained about how the cues will go. At London Airport, Brains tells Tin-Tin that Skythrust should have left Paris by now. He says they'll go up to the control tower to pay their respects, then they'll go down to the runway and meet the plane.

In the Skythrust, the fashion show has begun. Lemaire takes to the stage and talks about his new collection, including about the fact that everything is made out of Penelon. One of the buyers onboard says this Penelon is the biggest thing in fabric development since the cotton mill. Lemaire continues to have his models wear different outfits, including Alligator Attack -one which is strictly for wearing after dark. In the cockpit, the co-pilot says that are now 15 minutes away from London Airport.

In the control tower, Burroughs says they have them on their radar. He provides them with a provisional runway to land on and says Mr. Hackenbacker is here, who sends his best. Meanwhile, everyone is congratulating Lemaire on his show. Penelope says she must go and change, as they'll be flying into London soon. Deirdre asks where Madeline has got to, but Lemaire says he doesn't have a clue. Madeline has gone up to the cockpit, to thank the pilots for such a smooth flight.

However she then pulls out a gun and tells them to leave the controls just as they are. She says this is just the end of part one, part two of the journey is just beginning. The plans have been changed and they are now not going to London. She hands Ashton some documents and says this is their new destination. Ashton says this is in the middle of the Sahara, miles from anywhere. Madeline says precisely -there will be no one round to disturb them. She tells them to set a course, as they don't have time to waste. Skythrust turns around.

Elsewhere, Mason has also pulled out a gun and says nobody in this aircraft is going to get hurt, as long as they're sensible. He tells everyone there has just been a slight change in plans, as they are not going to London after all. He tells Lemaire to get those dresses boxed up again. This Penelon stuff is too good a haul to lose! In the cockpit, Madeline tells the pilots not to try and use the radio, it won't do them much good anyway -there isn't a person in this world who can help.

Lemaire says they must do something. Penelope says there is one chance. She twists a ring on her finger, which sets off a signal received at Tracy Island. Jeff says he thought it was a little too peaceful around here. He tells Scott and Virgil to go, and also says he'll have Alan sent down to Thunderbird 2.

A little later, Thunderbird 1 takes off, followed by Thunderbird 2. Jeff says he'll contact Brains in London to see if he has any idea to what's gone wrong. He asks them to give him a bearing on Penelope's signal as soon as they can.

Lemaire wonders where they are been taken, but Penelope tells him to be patient -help is on its way. Mason tells them to just sit nice and quiet. Penelope warns him that this aircraft will soon be tracked down. Mason tells her she's wrong, as they're handling all radio calls now. In Thunderbird 1, Scott reports that he has a bearing on Skythrust, and tells his father what it is.

Virgil then reports he has an exact fix, and says what it is. Jeff looks at a map and says it looks like Skythrust is heading for the Sahara, although why would anyone hijack a plane and take it there? In the Sahara, two guys called Ross and Collins are waiting for the Skythrust to arrive. Ross complains about the sand, but Collins tells him to stop griping and get on the radio. Ross tries to get through to Skythrust, but there's no answer. Collins assures him they'll be here.

Madeline says to switch on the radio, as they're nearing their destination. They hear a call from International Rescue, so Madeline tells the pilots not to answer it. Scott keeps trying to contact them, so Ashton says they'd better answer it, as International Rescue never gives up. Madeline lets him but tells him to watch what he says. Scott asks them to head to London, but Ashton says they can't. Scott insists, so Madeline takes the radio and asks what'll happen if they refuses. Scott says they'll take action to force them to, but Madeline calls his bluff. She knows International Rescue's job is to save lives, not risk them. She tells Scott to leave them alone. Scott contacts his father and lets him know what's happened. Jeff tells him that Brains has an idea, one he's telling Virgil about now.

Brains tells Virgil that what he's about to say may sound crazy, but he has a hunch it'll work. He tells him to load up a low velocity, non-explosive missile and take a pot shot at Skythrust's undercart. Back in Skythrust, Madeline contacts Ross and Collins, telling them that they'll be with them in eight minutes. She says that no one is going to stop them now, not even International Rescue. Thunderbird 2 then makes makes several passes by Skythrust, making the plane shake.

Madeline uses the radio to contact Thunderbird 2. She says she has Ashton and the co-pilot right here, and if International Rescue are still in sight 30 seconds from now, Ashton gets a bullet through the brain. Mason tells everyone not to build their hopes up, as it looks like the mighty International Rescue are giving up. Thunderbird 2 moves away from Skythrust, so Virgil tells Alan it looks like they'll have to use Brains' idea.

Thunderbird 2 turns back around and chases after Skythrust. Virgil moves Thunderbird 2 in closer as a missile is loaded up, which Alan aims at Skythrust. He fires the missile, which hits the undercart of the plane and causes damage to it. In the cockpit, the co-pilot says the wheel housing is locked. He tries again but says it's no good, it won't free itself.

Ashton says this means they can't land in the Sahara, not with an undercart malfunction. Madeline says not to try and blind her with science, so Ashton says to get Mason in here, who knows about these things. Mason is sent up and asks what's going on. Ashton shows him the undercart fault, and says that if he can tell him how to land this aircraft on a desert airstrip without wheels, he needs to tell him now. He then mentions what'll happen if they try -they have nearly 5,000 gallons of fuel on board, when that goes up, they won't even find the fillings in his teeth. Mason asks if they can even land at London. Ashton says at London they're fully equipped for emergency landings, so at least they'll have a chance.

Madeline comes back, and isn't happy to find out they're going to London. Mason tells her to shut up, as he's seen a plane go up, and he doesn't want to be in this one when it does. Alan contacts his father and says that the Skythrust is turning back. Jeff says he's just had some news from Interpol -the rendezvous was with two characters named Ross and Collins. These two both have long records and are wanted for murder among other things. He tells Alan and Virgil to pay them a call.

At London Airport, several emergency vehicles gather together on a runway. Tin-Tin sees them and tells Brains she's worried. But Brains says the fire trucks won't be needed. Tin-Tin asks what's so special about Skythrust, but Brains tells her to just wait and see. Skythrust arrives in England, and is 17 miles away from the airport.

Ashton says they've still got just under half their fuel left. Mason asks if they can jettison any, but Madeline tells him to pull himself together. As the pilots start to make the landing, Madeline asks if they can ditch any fuel like Mason suggested. Ashton says it can't be done and tells them that if they're so worried, they should go back to the rear, as it's the safest place. Mason and Madeline decide to do so. Skythrust then makes its landing without any wheels.

As the plane slides across the runway, part of it suddenly flies away separately. This is seen by Norman in the control tower, who tells Burroughs to take it up to 40,000 feet. Burroughs does so, then has the object detonate.

Skythrust eventually comes to a stop, but the plane has not exploded or even caught fire in any way. Norman says that Hackenbacker's ejectable fuel pod to eliminate fire hazards really works, and will revolutionize flying safely. Inside the Skythrust, Penelope says this was no worse than one or two conventional landings she's experienced.

Everyone sees Madeline and Mason cowering in a corner. Penelope says the two brave hijackers don't need to get up, they can just wait for the police. Lemaire asks about their accomplices, but Penelope thinks they'll be well taken care off. Meanwhile, Ross thinks something has happened and wants to get out of here before this storm gets any worse. Collins says they'll give them a few more minutes.

They then hear what they believe is to be Skythrust, but it's actually Thunderbird 2. They think it's a great looking plane, but as they watch it come in again, it fires a missile at them! Their truck is blown up, sending the two flying.

Jeff tells Alan and Virgil well done. Jeff tells Gordon that just about wraps the whole thing up. In the control tower, Norman says this hasn't been a day they'll forget about in a hurry. Brains says they should all go over to the Starlight Roof and have a bite to eat, as he's starving. Penelope says they've still got that bottle of champagne to open.

She says it's vintage 1993, which was the best year for champagne. Aston says they should go and grab a table. As everyone starts to leave, Brains asks Tin-Tin if he could escort her to the Starlight Roof. Tin-Tin says she'd be delighted for Mr. Hackenbacker to do that, but he tells her she can call him Hyram.