When the new, fully-automated Pacific Monorail goes into action, it'll make its investors rich - provided it ever actually goes into action. Determined to find investors, the president of the corporation starts hunting around, starting with the well-known Lady Penelope Creighton-Ward. While Lady Penelope has no interest in the project, she directs the president to her friend Jeff Tracy.
Unbeknownst to Lady Penelope, the president had taken the opportunity to case her house - and disable the alarms - prior to calling in his more criminal friends. While the president takes Jeff, Tin Tin and Brains on a demonstration tour of the new monorail, the criminals break into Creighton Manor and the safe beneath the drawing room. While they succeed in removing Lady Penelope's famous jewelry, the safe's alarm system is on an independent circuit, and her ladyship and her loyal butler Parker are alerted to their presence. Armed with machine guns, they disable the criminals' getaway car, forcing them to hotwire the bright pink Rolls-Royce FAB 1. Sadly for the crooks, FAB 1 can be remotely controlled by Lady Penelope's bedside lamp. Leaving them to drive in circles around the fountain until morning, Lady Penelope and Parker retire to bed.
On the monorail, however, things are not going as smoothly. A storm drives a helijet into the support column of a bridge, severely damaging it. The automatic signalling equipment is damaged, and the onrushing monorail will not stop until it plunges into the abyss. The Thunderbirds race to the scene to save their family - while striving to retain their cover over the radio link.
- Action Girl: Lady Penelope is at her most Badass here.
- Break the Haughty: Happens to Grafton, twice. First, he insists the monorail is perfectly safe (for its cost anyway). Of course, that turns out about as well as you'd expect in a Thunderbirds episode. Then, after he's been saved, he insists he'll be albe to keep his ass out of jail. This doesn't fare much better.
- Collision Damage: how the bridge gets damaged.
- Corrupt Corporate Executive: Warren Grafton, the president of the monorail company; he and his associates use illegal ways to get their fundings, like burglary and fraude, and he evidently cares more about making profit than the safety of his monorail.
- Gentleman Snarker: Jeff gets pretty snarky towards Grafton, and becomes increasingly less polite about it as his patience wears off.
- Humiliation Conga: What Lady Penelope puts the burglars through.
- No OSHA Compliance: the monorail; everything about it is automatic, with no possibility for a human engineer to override the computer and take over control of the train himself. There isn't even something like a manual controlled emergency break; Brains and Tin Tin have to make one on the spot after the train goes haywire. Although Thunderbirds is no stranger to this trope, this is one of the rare cases where it is lampshaded.
- Runaway Train: the "totally safe" monorail becomes one after the bridge is damaged and the automatic signals are interrupted.
- Tempting Fate / Gilligan Cut: at the end of the episode, Warren Grafton brags how he will never go to jail despite all that has happened. Next scene shows him and his associates in prison.
- Tempting Fate is practically Grafton's defining character trait along with being a Corrupt Corporate Executive. He keeps insisting nothing can go wrong with his train to the extent that Jeff and Brains aren't wondering if an accident will happen, but when.
- Women Drivers: Averted; in sharp contrast to her previous driving experience in "Vault of Death", Lady Penelope actually drives very well in this episode even while being chased by two crooks.
- What Could Possibly Go Wrong?: Warren Grafton keeps insisting his monorail is absolutely safe. Jeff and Brains are not convinced, and are proven right.