Somewhere in France, Penelope and Parker are at a casino. Penelope seems to be doing well, but she then hears someone else nearby.That someone is the Duchess of Royston, who is gambling but doing terribly, saying she has lost over 750,000. Penelope tells Parker to take over whilst she talks to the Duchess. Meanwhile the Duchess puts everything on 17 black.
What the Duchess doesn't know is that the roulette table she is at is rigged, as the guy operating it has a method of picking which number and colour the ball will land on. It lands on 18 red, and the Duchess is out of money. So she puts on some of her jewellery instead. Two guys opposite her can't believe how stupid she is.
Penelope comes across and the Duchess says it is a delightful surprise to see her again. She explains how poorly she is doing money wise and that the only thing she has left which is worth anything is her Braquasso painting. The two guys opposite her, Chandler and Brophy, hear this and become interested, as Braquasso paintings are worth a lot. The rigged roulette then stops spinning, and the Duchess has lost again. However Penelope says the table is fixed. The croupier says she is mistaken, but hits a button that sends a signal to his boss. The boss cuts the power and all of the lights switch off, whilst he quickly shoves all of the money he's made into a bag.Parker says to the boss that the game is up and points a gun at him. The boss dives under his desk and starts shooting, so Parker shoots back. The boss eventually gets away by going through a secret passageway in a wall, which closes behind him. Parker doesn't know how to get it to open.
Penelope enters and finds out the crooked owner of the casino has escaped, and she has also lost sight of the Duchess. She tells Parker they will go after the boss. The boss and one of the croupiers get into a car. Penelope and Parker see them drive off, and go after them in FAB 1.
When the casino boss sees that they are being followed, he opens fire with a machinegun, but the bullets do no damage to FAB 1. Parker returns fire, but due to all the bends in the road, his bullets miss the mark. The casino boss and croupier manage to get far enough away to make a quick turn, without being seen. They hide in a building.
Penelope decides to find the Duchess and goes to the hotel she said she was staying at. However, Penelope finds out from a receptionist that the Duchess has left, and thinks she mentioned she was going to Western Castle, in England. Penelope and Parker return to England, and head to the Duchess' home, but see it is for sale. Penelope realises that the Deborah really has lost everything. She hopes they can help her somehow and remembers that Jeff Tracy is coming over to watch the air show with her. Maybe he'll think of something, giving his forte is rescues.A short time later, Jeff is at London Airport with Penelope at the air show. The jet he wanted to see is in the skies -a new carrier. The crowd watches as a second, smaller plane moves in closer to the new carrier jet, and amazingly, lands on it.
The pilot of the carrier then ejects, but the pilot of the smaller plane has full control and safely lands the carrier on a runway. Some military Generals are impressed but think that International Rescue do this thing all of the time. Jeff and Penelope decide to keep quiet. Later on, the two of them head to an art exhibition.
The exhibition features a lot of 20th century art. Inside it, Penelope mentions the Duchess, a friend of hers who is out of money due to trying to conquer the French market and failing. The only valuable thing the Duchess now has is her Braquasso painting. Jeff takes a look at the painting, which features a gazelle. Jeff says he knows someone who may be interesting in purchasing it, and flies out to New York.
Jeff goes to a place called Gazelle Automations Incorporated, where he meets an old friend of his who happens to be the boss of the company - Wilbur Dandridge III. Wilbur loves automating things, and when he offers Jeff a cigarette, a whole bunch of them appear out of his desk, already lit up.He then offers him a drink, and when Jeff asks for whiskey, he gets it without having to even get up. Jeff then explains the point of his visit and shows Wilbur a reproduction of "Portrait of a Gazelle", the Braquasso painting the Duchess owns. When Wilbur sees it he desperately wants it, as he loves gazelles and thinks this one could be the symbol of his company.
Wilbur goes to England, and visits Penelope. The Duchess has been staying with her, and also has the painting with her there. Wilbur sits down and offers the Duchess £475,000 for the painting, but she says it is not for sale. The Duchess doesn't think his offer is enough, so he ups it and says he is willing to pay £600,000 for the painting. The Duchess still refuses, saying that is precious to her and she cannot sell it. Wilbur says he came all the way from America to get this painting. Penelope says they can come to a compromise. She suggests that the Duchess should let Wilbur rent the painting for a limited time, such as six months, then he can return it to her. Wilbur thinks this is a great idea, and the Duchess seems to be alright with it. A few days later, a Fireflash jet is scheduled to fly to New York. The Duchess is going to be on it, as she wants to deliver the painting to Mr. Dandridge personally. Before she gets on the Fireflash, Penelope gives her a St Christopher and tells her to wear it, as it will bring her luck. The Duchess thanks her for her help and then says farewell, as she gets onboard the Fireflash.
Captain Hanson and the Fireflash co-pilot are ready to take off, and minutes later the Fireflash is in the air. The Duchess takes a look at the St Christopher broach Penelope gave her, and puts it on.The broach actually has a transmitter inside it, and as Penelope and Parker head back home in FAB 1, Penelope can see where the Duchess is on a map screen. Meanwhile, in America, Wilbur tells his driver Hendricks to go to the airport and pick up the Duchess, and to give her that cheque to show he means business. As Hendricks hangs up, he is hit on the back of the head and knocked out - Chandler and Brophy are the ones responsible, and they plan to get that painting.
The Fireflash lands at New York Central Airport. The Duchess gets her bag and painting, and is then met by Brophy. She has no idea who he really is, and so goes with him. She thinks she is going to New York, but Brophy explains to her that Mr. Dandridge has asked for her to be taken to his house in the countryside.Back in England, Penelope and Parker are using a map to see where the Duchess is, and are alarmed when they see her moving away from New York. Penelope contacts Wilbur, who says he was about to contact her -the Duchess has not arrived, and she is really overdue. Penelope believes that the Duchess has been kidnapped, but then she loses the signal to Wilbur. She instead contacts Jeff, who tells her not to worry.
Jeff has Thunderbird 1 and Thunderbird 2 take off. Parker says that the Duchess seems to have stopped moving, as her signal is staying in the same place. On Thunderbird 5, John picks up the signal and finds the exact location of the Duchess, and passes this information on to Scott and Virgil. Meanwhile, Brophy has driven the Duchess to a battered old house out in the middle of nowhere.
Brophy ties the Duchess to a chair and says he'll be going now. The Duchess asks what he wants, but he says he already has it -her painting. He managed to slip it to his friend at the airport when she was exchanging her money. They are going to get away with this just as those crooks got away with her money at the casino. The Duchess says she thought she had seen him before and realises he was at the casino, on her table, a few days a go. Brophy then leaves, but has lots of gas released -he advises that she shouldn't light any matches.
The Duchess starts to cough and realises she needs to get out of here. She starts trying to get off the chair, but is so clumsy she hits a ladder, which crashes back into a generator and smashes it, causing an explosion. Scott arrives at the co-ordinates John gave him, and sees a house below.
This house then explodes, and Scott reports this to his father. John tells Scott that the Duchess' broach transmitter is still working, and incredibly, the Duchess is still alive. Meanwhile, Wilbur is told that someone is here with the painting. He knows that whoever it is must be a crook, and tells his secretary to call the police.Chandler enters the room and Wilbur is pleased to see the painting. Chandler says he represents the Duchess, and wants the second payment instalment in cash. Wilbur gets a box out with some cash in it, but it also contains a gun. He pulls the gun out and tells Chandler not to move, but he throws the painting at him. Wilbur accidentally pulls the trigger and the bullet ends up ruining the painting. Meanwhile, part of the house explodes, and Scott lands Thunderbird 1. He sees that the Duchess' signal is coming from under the ground, so she must be in the house's cellar. He tells Virgil that they are going to need to use the Mole to get underground. Virgil lands Thunderbird 2, and moments later the Mole drives out of pod 3. Meanwhile, inside the cellar, the Duchess has managed to get the ropes off, but is then struck on the head by some debris, and she collapses. Virgil gets the Mole to go underground, and Scott gives him the precise co-ordinates for where he needs to go. Meanwhile, Scott has seen that only one wall of the house is left standing -and if it topples over, the cellar will never take the weight of it. He drives a vehicle called the Domo out of pod 3, and moves it up to the wall. The Domo has three powerful suction cups, which Scott uses to keep the wall from falling over. The Duchess wakes up just as the Mole comes crashing through one of the cellar walls. Virgil tells her to hurry and come this way. The Duchess leaves, but is sure to grab her umbrella first. As they head back up, the wall falls away from the Domo and smashes through the cellar. Scott reports this back to Tracy Island and says that he can't get through to Virgil yet. However the Mole then appears, and later on the Duchess is taken to hospital. She tells Penelope that she has been able to buy back her home with the cheque she received from Mr. Dandridge, but Penelope says she has some bad news about the painting. The Duchess doesn't want to hear it -she has been saved by International Rescue, the FBI have arrested the men who stole her painting, and Interpol have closed down the crooked casino -she will be getting back all of the money she lost there.
Wilbur then walks in and says he has some bad news about her painting -he accidentally destroyed it. The Duchess does not seem shocked at this news, and takes a roll out of her umbrella. The Duchess reveals she has always had the real painting with her, the one Wilbur destroyed was a fake. She tells him he can have the real one on loan for six months as long as he gives her the second payment.
Parker then walks in and says that a magazine wants to buy the rights to her life story for £30,000. She wants £50,000, and then asks who won the horse race. Parker tells her that it was won by Desperate Intruder -sadly not the horse she had bet on. She says that once she is up and about again, she wants to go on a trip. And some time later, the Duchess has been on her trip - to another casino!