Whilst at a casino, Penelope comes across her old friend, the Duchess of Royston. The Duchess is playing at a rigged table, and loses practically everything she has. Penelope calls out that the table is rigged, but the casino owner is alerted and makes a run for it. Penelope and Parker follow him, but they eventually lose him. Penelope decides to go back and console the Duchess, only to find that she's already checked out of her hotel and has gone back to England.

Wanting to help the Duchess, Penelope decides to bring it up when Jeff Tracy comes over to go an an air display with her. After seeing a new carrier aircraft at the air display, the two go to a museum, where the Duchess' only remaining prize posession is on display: "Portrait of a Gazelle", a valuable painting by Braquasso. Jeff thinks he knows someone who would be interested in it, and goes to New York to meet the owner of Gazelle Automations Inc, Wilbur Dandridge the Third. After seeing a reproduction of the painting, Wilbur decides he wants it no matter what.

He flies to England and tries to buy the painting for hundreds of thousands of pounds, but the Duchess insists it isn't for sale. Penelope comes up with a compromise, and suggests that Wilbur could rent the painting for six months. The Duchess agrees to this, and decides to take the painting to America herself to present it to Wilbur. She goes to London Airport, where Penelope gives her a broach which secretly has a homing device in it. The Duchess flies to New York on a Fireflash plane, where she is due to meet Wilbur's chauffeur, Hendrix. However, Hendrix gets knocked out by Chandler and Brophy, two people who witnessed the Duchess' antics in the casino and know about her painting. Brophy goes to collect the Duchess.

In England, Penelope and Parker watch the signal, but become concerned when they realize the Duchess is moving away from New York City. Penelope contacts Wilbur, who says he doesn't know where the Duchess is, as she never arrived. The video feed is then cut off, so Penelope contacts Jeff. Jeff has Thunderbirds 1 and 2 sent out, and John relays to Scott and Virgil the location of the Duchess.

Brophy takes the Duchess to a house and ties her up in the basement. He then leaves, telling her that Chandler has taken the painting already. The basement is filling up with gas, and the Duchess accidentally causes an explosion that destroys most of the house. Scott arrives just in time to see it, but finds out that the Duchess' signal is still transmitting. Meanwhile, Chandler takes the picture to Wilbur to try and get the cash payment from him, but WIlbur is onto his game.

WIlbur pulls out a gun, but Chandler throws the painting at him, leading to it getting badly damaged by a bullet. Thunderbird 2 arrives at the house, and Virgil uses the Mole to start drilling into the ground to reach the basement. The house has almost completely collapsed other than one wall, which is in danger of falling down over the basement. Scott uses the Domo to prevent it from falling.

Virgil gets into the house and saves the Duchess. They return to the Mole which returns to the surface, just before the wall falls away from the Domo and destroys the basement. The Duchess is taken to a hospital, happy how things have turned out -the men who took her painting were both caught, and Interpol have also arrested the crooked casino workers, leading to her getting her money back. Wilbur then arrives and reveals what happened to the painting, but the Duchess says she has news for him.

She pulls something wrapped up inside her umbrella, which Penelope opens up. It's the painting -the Duchess has the real one with her all along! She says Wilbur can have it for the next sixth months once he's paid her. Parker then tells her a magazine wants the rights to her life story, which she says they can have for 50,000 pounds -no less. She then enquires about a horse race she'd bet on, but Parker says she didn't win. The Duchess decides once she's up and about again there's a place she'll have to go, and is soon back in another casino.

Notes

-Originally, the Duchess was going to be voiced by Christine Finn (Tin-Tin's voice actress), and then Sylvia Anderson (Penelope's voice actress) but neither of them could do a suitable voice. In the end Ray Barrett (John's voice actor) said he'd do the voice, surprising everyone, but after he demonstrated the voice he would use, he was given the part.

-The episode uses a huge amount of different puppets, most of which only appear in the background. One of the shots during the opening casino scene has around 18 puppets on screen at once.

-At the art exhibition, one of the paintings is Virgil's portrait of Alan from Move - And You're Dead.

-During the air display, the shot of the pilot parachuting is reused footage from Trapped in the Sky.

-The shots of the Fireflash used in this episode are reused from Trapped in the Sky as well.

-The Domo vehicle Scott uses was previously used in Martian Invasion as the Excavator, but has been changed slightly so it now has the suction cups on it. The Domo is not named in in the episode, but this is what it's called in some of the Thunderbirds books.

-The name of the horse Parker mentions is a most likely a reference to the episode of the same name.

Errors

-Most of the crooked croupier's dialogue is provided by Matt Zimmerman, but one line -"Dix-huit rouge, 18 red" -is said by Peter Dyneley.
-The pod door has "3" on it, but if you look inside it when the Mole drives out, you can see a banner stating "Thunderbird 2 Pod 4".