When the elderly Duchess of Royston loses everything at a casino in Monte Carlo, her friend Lady Penelope decides to help her. Enlisting Jeff Tracy's extensive contacts, Lady Penelope finds someone interested in purchasing the Duchess' last asset: Braquasso's "Portrait of a Gazelle". However, two crooks working for a crime syndicate (who witnessed the duchess being conned at the casino), kidnap the embattled aristocrat and make off with the painting, leaving her in a deserted house that is leaking gas. Can International Rescue save the Duchess before she falls victim to the ensuing inferno?
- Abandoned Area: The art thieves leave the titular duchess tied up in the basement of an abandoned country house. This is only the start of her problems...
- A Day in the Limelight: This is one of the most Penelope-centered episodes of the series. None of the Tracy brothers appear until two-thirds of the way in.
- Bookends: The episode begins and ends at the casino (with the Duchess gambling at roulette).
- Break the Fake: The Portrait of a Gazelle — the painting around which the whole episode revolves — is apparently destroyed in a gunfight. The Duchess later reveals that the wrecked version is only a copy: she has been carrying the real thing in her umbrella the whole time.
- The Cameo: There's a cameo by the Fireflash, from the first episode. It consists entirely of Stock Footage from that episode.
- Casino Episode: The first act takes place at The Casino, where Lady Penelope encounters her hapless friend Deborah, the Duchess of Royston, being swindled out of the last of her money — and her jewellery. The final scene shows the Duchess, her riches restored, at another casino, though hopefully a more honest one.
- Chekhov's Blind: Dandridge's office blind is faulty and often closes noisily without warning - Dandridge says he means to get it fixed. Later, when attempting to confront a criminal who has the Portrait of a Gazelle, it drops on cue and startles them, causing the painting to get a bullet through it. It's actually a reproduction.
- Collector of the Strange: Dandridge has a strange obsession with gazelles. He named his company "Gazelle Enterprises" and themed his entire office after gazelles. Nobody bats an eye at this.
- Composite Character: - Braquasso is basically George Bracque and Pablo Picasso merged into a single artist. Both were highly influential before World War One though, as they developed Cubism pretty much by themselves.
- Contrived Coincidence: Lady Penelope happens to bump into her friend the Duchess of Royston just as she gambling away the last of her money.
- Conveniently Timed Distraction: The stuck blind in Dandridge's office suddenly unstick itself just as he has the crook at gunpoint. The crook takes advantage of Dandridge's lapse in attention by throwing the painting at him to make his escape.
- Cool, but Inefficient: Dandridge exemplifies this with his insistence on computerised automation of every part of his building, even when there is no apparent benefit. The best example is the electronic blind, which gets stuck every time it is used.
- Cross-Dressing Voice: Ray Barrett is having the time of his life as the Duchess. Recording sessions for this episode were reportedly hilarious.
- Drill Tank: The Mole's third appearance.
- Fixing the Game: The roulette table that the Duchess is gambling on is rigged: the ball only lands on red numbers (the Duchess keeps betting on '17 Black') when the dealers press a hidden button.
- The Gambling Addict: The Duchess.
- Here We Go Again!: The Duchess has learned nothing from her mistakes and ends the episode once more in a casino...
- Large Ham: The Duchess. Not only is her puppet one of the most caricatured in the series, Ray Barrett is having WAY too much fun doing her voice.
- Machine Monotone: The Lift in the building of the buyer basically sounds like a non-malicious Dalek (voiced by the same guy, too). With a twist, in that machines were totally not expected to be able to reciprocate pleasantries. In a sense, it is still impressive when one considers the necessities for processing the vocal input.
- MacGuffin: The Portrait of a Gazelle, that the bad guys want to get their hands on and which is the only object of value that the Duchess has left after her disastrous evening at the Casino.
- Mythology Gag: A rather odd one: there is mention of a racehorse named "Desperate Intruder", the title of a previous Thunderbirds episode.
- Properly Paranoid: Lady Penelope worries that the Duchess' troubles aren't over yet when she departs for New York with her painting and decides to keep a close eye on her by giving her a St. Christopher brooch, that hides a tracking device. Her suspicions turn out to be correct.
- The Duchess herself also took precautions, by hiding the real painting in her umbrella and putting a reproduction in her luggage.
- Quintessential British Gentleman: When going undercover with Lady Penelope to attend an air show, Jeff dons a top hat and puts on an outrageously aristocratic English accent. He falls down, unfortunately, on allowing enthusiasm to creep into his voice.
- Tracking Device: Lady Penelope uses one to keep track of the Duchess during her trip to New York, hidden in the brooch as mentioned. This turns out to be a good thing since she is abducted.
