"Tracy, something's gone wrong. We're heading for trouble - and I mean trouble!"

International Rescue become involved with Warren Grafton's crooked organization who will go to any lengths to ensure the completion of their new monorail line. While Grafton's men attempt to raid the Creighton-Ward Mansion, Jeff, Brains and Tin-Tin take a ride on the monorail only for their train to end up heading for disaster...

One day a car pulls up at the Creighton-Ward Mansion. Parker answers the door to Warren Grafton, a man who has an appointment with Lady Penelope. Parker explains that Penelope will be a little late and shows Grafton into a room to wait. Using A statue, he then contacts Penelope who is driving FAB 1. She tells him that she is being tailed.

A car containing a pair of crooks pulls up alongside FAB 1 and one of them motions for Penelope to pull over with a gun. She speeds away and attempts to lose them with a thick black cloud but they have radar assisted steering and still manage to follow. Next she lays out some grease on the road but using retractable tyre studs they are able to overcome this also. One of them produces a machine gun and begins firing. Penelope fires back and their car skids off the road and explodes.

Meanwhile Grafton uses a fake cigarette lighter to detect the location of the jewels hidden in the room; they are under the floor. He attaches a device to the inside of the window to deactivate the alarm. Penelope arrives and apologizes for her late arrival. Grafton is searching for investors for his new completely automatic Pacific-Atlantic Monorail, 500 miles of which is already built. Parker brings in a fake telegram for Penelope telling her that Grafton's driver is a criminal. Penelope suggests that a friend of hers would be in a better position to fund the monorail.

Grafton leaves and explains to Malloy, his chauffeur, that they are already to make Penelope pay. Parker tells Penelope of his meeting with Malloy in prison. Penelope contacts Jeff and tells him about Grafton's proposal. Scott recalls that the monorail has been in trouble over safety precautions.

In New York, Grafton meets with his fellow crooks who, through a variety of unlawful activities, have already managed to raise 21 of the $40 million needed for the monorail. While Grafton will take Jeff and his advisors on the monotrain the next day, Malloy and Selsden will raid the Creighton-Ward Mansion.

Next day Jeff, Brains and Tin-Tin are taken for a ride by Grafton. He assures them that their is no risk associated with the entirely automated systems. If anything were to go wrong, the patrolling helijets would report it.

Patrol 304 is passing over a bridge further down the line when a storm begins. Suddenly a fork of lightning strikes the helijet and Joe, the pilot, is forced to eject. The helijet crashes into one of the bridge support columns, leaving the bridge unstable and the autmatic signals deactivated. Joe's parachute becomes caught on the side of the bridge, leaving him suspended and unable to call for help.

Grafton is continuing to show off the monotrain but Jeff is unimpressed with his small regard for people. Brains and Tin-Tin examine the controlling computer in the leading coach. The next helijet arrives at the collapsing bridge and Joe waves its pilot Stan to his position. Joe insists that Stan radio the train before rescuing him; if it isn't stopped all of the passengers will be killed. While Grafton recieves Stan's call, the International Rescue team discuss their unease with Grafton's apparent disregard for human life.

Under the cover of darkness in England, Malloy and Selsden drive up to the Creighton-Ward Mansion and break through the door. Penelope and Parker are both asleep. As the monotrain hurtles towards its doom, Grafton confesses about the bridge to Jeff. As Joe is winched away, an entire section of the bridge collapses. Brains and Tin-Tin begin work at the computer in the hope that they can stop the train.

Malloy and Selsden enter the room containing the jewels. Peeling the rug off the floor, they uncover a safe. Jeff suggests to Grafton calling International Rescue. Brains' first attempt to stop the train fails. Jeff calls Thunderbird 5, identifying himself as 'Tracy' and reporting the trouble. John catches on and pretends not to know him. Scott takes off in Thunderbird 1 with Virgil following in Thunderbird 2.

Selsden cracks the safe, but unknown to the crooks, it activates a second alarm system which only Penelope and Parker hear. The robbers pile the jewels into their bags and make a hurried exit. As they attempt to drive away, Penelope and Parker shoot at them from nearby windows. Parker hits the tyres. Selsden and Malloy abduct FAB 1 but using remote control, Penelope makes the car drive constantly around a statue all night.

Joe and Stan see the monotrain on the horizon. Brains makes one final attempt to stop the train. The brakes activate but the train is still going too fast. It hurtles onto the bridge then grinds to a halt, just in front of the missing track. Thunderbird 1 arrives and Scott tells them that the bridge could be totally destroyed at any time. He urges them to go to the rear carriage but just as Grafton is about to step out onto the walkway, it collapses as well.

With the passengers now aboard the centre carriage, Thunderbird 2 arrives and Virgil lowers the grabs and picks it up, away from the rest of the train. The coach is flown clear just as the bridge and the rest of the train plummets to the bottom of the ravine.

Thunderbird 2 leaves the coach safely on the ground and follows Thunderbird 1 back to Tracy Island. Grafton is sceptical when Jeff tells him that he will soon end up in prison. Soon he is opening a new line of his monorail; at least in a fantasy in his cell.

Verdict: The introduction of the monorail shows it to be a focus of incredible tension as it speeds towards disaster as in the semi-sequel, The Perils Of Penelope. The two parallel plots of this story work well on their own (particually the monorail disaster) but they are so unalike that they don't quite gell together.

DVD availability: On Volume 6 and the Complete Box Set.

VHS availability: On the Pod 2 Box Set and the Complete Box Set.

Novel availability: Brink Of Disaster by Dave Morris.