Tom Prescott is driving home when he comes across a hitchhiker. The guy asks him if he's going anywhere near Princeton Avenue, so he says he can give him a lift. The hitchhiker gets in his car, and the two drive off. Tom asks him if he lives down Princeton Avenue, as it's a nice quiet neighborhood. The hitchhiker says he doesn't, but his doctor does, he just needs to get him down to see his wife as she's real sick -what a night for his car battery to go flat. He thinks he was lucky to have found Tom, and asks him if he's married too.

Tom says he sure is, and it's in fact their third wedding anniversary today. The hitchhiker says that explains the little flower display on the backseat. Tom says as soon as the babysitter drops round, he's going out for a meal with his wife. He then asks the hitchhiker why he didn't just phone for the doctor. The hitchhiker quickly changes the subject by saying he wants to be dropped off here. Tom stops his car, but the hitchhiker says he's got something for him.

He puts a bracelet on his wrist and pulls out a gun. He tells Prescott to listen to him. Tom asks how he knew his name, but the hitchhiker says to never mind about that. He tells him to listen to what he's going to say carefully, as he doesn't have time to repeat. He knows he works in the Hudson Building, in room 1972. He instructs him to go there and look in the top drawer of his cabinet, as he'll find a key for the bracelet. Tom tries to get the bracelet off, but the hitchhiker tells him he's wasting time. That bracelet is made out of hyrdo-chromatised steel, which won't break under 20,000 degrees of heat. The box on it contains an explosive charge, which is set to go off soon. He tells him to go to his room in the Hudson Building, and when he gets the key, he is to take the bracelet off and leave it in the same drawer. Then, the whole place goes up. Tom thinks he's crazy, but he tells him he doesn't have time to argue -that bomb goes off in 21 minutes. If he doesn't get that bracelet off soon, his wife is going to be a widow on her third wedding anniversary. The hitchhiker then gets out of the car and tells him not to throw the bracelet out of the office window -he'll want to get further away than that.

He then tells him that bomb is set for eight o'clock, and he's got 30 miles to go. Tom starts his car up and turns it around. He then starts driving very fast, heading through a town. He is seen speeding by police officers Flanagan and Jones, who start chasing after him in their patrol car. Flanagan reports to highway control that they are going in pursuit of a red car. They arrange for a barrier to be setup.

However, Tom drives right through it. His car is still in one piece, and he drives it to the Hudson Building. As he stops, he is seen by someone in the building opposite. It's Sam, the Hudson Building's janitor. He recognizes Tom's car and guesses he must have his own key with him.

But he then notices the police car drive up, and thinks the cops must have been after Tom. Tom has already entered the building, with less than 10 minutes to go. He calls for the elevator, which takes a long time to arrive. Meanwhile, Sam calls the police and tells them about what he saw.

Outside the Hudson Building, Flanagan and Jones have seen Tom's car. They look up at the building and see a light is on on one of the floors. Inside, Tom gets to the cabinet, and starts frantically searching through the top drawer to find the key. He eventually finds it, but sees the time and realizes he has less than a couple of minutes. Flanagan and Jones get to the building's front entrance, and wait for Sam to bring them a key.

Tom places the bracelet and key back in the drawer, before returning to the elevator. It starts to slowly descend, but as Tom checks his watches, he realizes that there are only a few seconds left. The bracelet's explosive charge then detonates, causing a large explosion which blows up most of the floor. The fire quickly starts spreading to other floors.

The elevator Tom is in suddenly drops. Flanagan is contacted by police commissioner Garfield, who tells him that as soon as the situation is under control, he wants a full rundown. That Hudson Building is government property, so they can't afford any security slip ups. Flanagan says the fire is getting worse, and whilst the fire department are on their way, the building's automatic extinguishers aren't working. They can't find the guy who started all this either, but he believes he must have gotten hit by the explosion. The elevator is out of action and they can't get near the scene of the explosion.

From Thunderbird 5, John contacts Tracy Island and tells them about the situation at the Hudson Building. He says the fire department are there now, but they're not having much success. Jeff asks what Brains makes of it. John says Brains believes only an incendiary explosion could cause so much fire so quickly. A news cast then comes through about the fire. The reporter says the fire department are desperately trying to cope with this mystery fire at the Hudson Building, which has completely destroyed the top five floors. The janitor has said that before the explosion, he saw Hudson employee Thomas Prescott arrive. Police commissioner Garfield has stated that they have several charges to make against Prescott, if they ever get him out of the inferno alive. The fire department have said their first attempts to rescue him have failed, and they are not optimistic about the auxiliary equipment they are now going to bring in.

Jeff says if that isn't a call to action, he doesn't know what is. He tells Alan to get Scott and Virgil down here, then tells Brains to put Virgil straight about which pod will be required. He then asks Tin-Tin to monitor all broadcasts about the fire at the Hudson Building, and keep Scott and Virgil informed. A short time later, Thunderbird 1 blasts off, followed by Thunderbird 2.

Brains tells Jeff he's given Virgil instructions about the necessary equipment. Judging by the latest reports, he's advised him to take an extra supply of dicetylene. At the building, the fire department continue to try and put out the fire. Flanagan tells Garfield that he doesn't hold out much hope for the guy at the bottom of the elevator shaft, as the place is getting badly flooded. The explosion caused the safety doors to shut automatically, but the fire has damaged the release mechanism and now they can't get them open.

Scott calls base and asks what the latest is. Tin-Tin says the fire department have stopped the fire from spreading, but they can't get it under control whilst Prescott is still at the bottom of the shaft. They also seem pretty certain the automatic fire extinguishers could not operate when the fire broke out because the main water supply had been cut off. Jeff asks Scott what his eta is. Scott says he should be reaching Spoke City in 9.5 minutes. At the building, Garfield arrives on the scene. Flanagan says they've contracted Prescott via the elevator radio, but he's in a bad way. There has also been a radio message for him: International Rescue are on their way.

Virgil says they will arrive at the rescue zone in 17 minutes. Jeff tells him Scott is practically there, and is talking to the police chief. Scott tells Garfield that if he can get the fire department to keep that fire under control, they can get the man out of the elevator shaft. Flanagan says the fire has spread to some of the basement floors next to the elevator shaft. There are 10 basement floors, and there is no other access to them due to the safety doors being jammed. Scott says they'll need part of the area cleared for landing. Garfield tells him to land in the open area behind the Hudson Building. Scott says he also wants his full guarantee of secrecy for his organization during this whole rescue operation. Garfield tells him he's got it.

Thunderbird 1 lands behind the building. At Tracy Island, Jeff and Tin-Tin listen to a radio report about International Rescue's arrival. The reporter says that, as requested by the International Rescue team, the entire rescue operation will be conducted in secret. Jeff says okay, but what about the man at the bottom of the shaft? In the elevator, Prescott has survived, but the elevator itself is flooding.

Garfield asks what those International Rescue guys are up to, they've been in there for 30 minutes. Scott tells his father that they've got the dicetylene cage fixed up. Virgil and Alan are inside the cage, which has been put into the elevator shaft. As it starts to move down, Alan says the heat is increasing. Virgil says he'll start the dicetylene sprinklers.

The dicetylene starts being poured all around the shaft. Alan thinks the dicetylene is great, Virgil says he just hopes their supply lasts -he doesn't think the tank is big enough. Scott asks them how it's going, and Virgil says alright so far, although he doubts their dicetylene supply will last. The cage continues to move down the shaft.

Virgil contacts Tom via the elevator radio. He says they've come to get him out of there, and asks what kind of shape the elevator is in. Tom says pretty bad, as the water is rising all the time. Virgil asks if the frame of the elevator car is still intact. Tom says he reckons it is. Virgil says he'll operate the grabs. A grab lowers down from the cage, and attaches to the elevator car. The cage then starts to move up the shaft, pulling the elevator car with it.

As the cage moves up, the dicetylene runs out. It moves through the fiery elevator shaft, but manages to get through the flames without dropping the elevator car. The elevator car is pulled up to the floor where Scott is. Scott tells Prescott that he's going to be alright now.

Later on, Flanagan goes to see Garfield. He tells him he has spoken to Prescott, who is still sticking to his story about the guy giving him the bracelet. Garfield says he's never heard an alibi like it, this guy has gone out on his wedding anniversary and committed enough offences to get him 20 years inside. Flanagan says Prescott has a spotless record, too. Garfield he says he believes Prescott's story. One, that explosion destroys the files on some of the most vicious gangs operating today, including the Erdman gang. Two, the automatic extinguishers in the building have been sabotaged. He thinks it adds up. Jones then enters the room, with something they'd found in the Hudson Building.

It's the bracelet, so Garfield tells Flanagan to get him the FBI -they'll get to the bottom of this, even if it means employing a little deception. Soon, newspapers carry a story about the death of Tom Prescott. Tin-Tin tells Alan she thought he'd said that he'd saved the man in the Hudson Building. Alan says they did, and asks his father what made them publish this story. Jeff thinks the authorities are taking this line for a very special reason. They must have some kind of a scheme lined up. Scott says that Prescott was a nice guy, and wishes they could help. Alan asks about doing that, but Jeff says no. This sort of thing is best left in the hands of the FBI and Interpol. His guess is they're trying to make the man responsible think it's safe to try the same trick again.

At the headquarters of the British Security Service, two men discuss who the best man for the job is. They choose Southern, who enters the room and throws his hat on the stand. Southern throws down his identification papers and is told that he won't be needing those. But he will need this: a radio hidden in a pen. Southern is told good luck, and to be careful.

Sometime later, Southern infiltrates the Erdman gang. He and two other members, Kenyon and Dempsey, wait in a castle. Dempsey wants to know why they're being kept here for, but Kenyon tells him to relax. Southern asks when they'll receive their instructions, as they've been waiting here for 36 hours. Just then, a voice comes through over the radio, who calls himself the leader. He says he'll now outline the final details of the plan. At 0900 hours, they are to leave the castle -the timing is vital. They are to drive to the nuclear plutonium store, which is marked on their route maps. Isotopes for all of Britain's nuclear power stations are stored inside the building. The authorities maintain that the store is impregnable, but they will prove them wrong. Powerful robots guard every door.

Kenyon asks if this means they won't run up against any people. The leader says the entire area is deserted, then says at 0910 hours they'll take up their positions before the perimeter gates. The alarm systems have already been rendered ineffectual, so they can move with ease. The ray machine they've been supplied with is tuned to the robot frequencies, which will render the robot inactive at the gate. They'll then enter the building, unsealing each door as they go. Again, they will use the ray machine against any robots. There are three electronic doors, with a robot guarding each. At 0930, they must be in the main storeroom where the vault is housed. They are to set fuses, then clear the area and drive south. They will then rendezvous with his helijet and prepare to leave the country.

Dempsey asks if that's when they get paid. The leader says yes -if their assignment has been successfully carried out. Southern asks if this means they'll meet the leader at last, and he says yes, if all has gone well, they will have earned that honor. Southern starts asking more questions, but Dempsey asks if he didn't hear the leader the first time, and he should stop playing around with that pen! He and Southern start to argue, but the leader tells them there is no time for bickering among themselves. Exact timing is vital, as three hours after the fuses have been set, at precisely 1230 hours, the nuclear store will explode. Southern asks about the fuses, wanting to know where to get a hold of them and what time to set them.

The leader says he was waiting for one of them to ask him that. He reveals that the fuses are set at this moment, and are attached to their wrists. Dempsey says this is crazy, as these bracelets are locked on, and they can't get them off! The leader says it is a precaution he's taken, to make certain they carry out the mission successfully. The key that will release the bracelets is the same one that unlocks the panel to the plutonium vault mechanism. It's inside the nuclear store, in a box on the vault door. Now they understand why they must get into that building and carry out the plan. If they fail, they'll all be blown to kingdom come! The call then ends. Kenyon thinks it was a smart move to lock these bracelets to their wrists. Southern tells them they need to get moving.

They drive to the nuclear store and take cover behind some rocks. Dempsey says they're bang on schedule, and tells Southern to fix that robot. Southern uses the ray machine, which emits a bright light. The robot at the gate sees it, but then falls over backwards after a few seconds. The group move in and open up the perimeter gates.

They get to the first sealed door. Kenyon tells Southern to get ready, because as soon as he works these frequencies, robot number two will try and grab them. He gets the door opened, and the robot sees them. It starts walking towards them, but Southern uses the ray machine to take it down. The group move up to the next door.

Kenyon gets the next door opened. The robot walks towards them, but is soon taken down by the ray machine. The group move into the room and head towards the next door. Dempsey says they've got ten minutes to find that key and get these fuses off their wrists. Kenyon gets the next door opened up.

But they see there is no robot inside the next room. Southern asks what happened to it, but Kenyon says who cares. They head inside the room. Kenyon tells Southern to get the key, as this fuse is worrying him. Dempsey says if these thing blow too soon, they're dead men. Southern gets the key, but also pulls out a gun. He tells Kenyon and Dempsey to stand where they are, as there's been a slight change of plan.

Kenyon and Dempsey want him to unlock these bracelets, but he says first, they're going to do something for him. They are to meet the leader as arranged, but they are to capture him and bring him here. Dempsey tells Southern he didn't like him from the start, and wishes he'd had him double checked. Southern says one of the first lessons in security is don't trust anyone. He tells them to get moving with those fuses, and bring the leader back -or they die. As he says this, the remaining robot shows up behind him. Dempsey starts wasting time by asking Southern if he wants a bigger cut. Kenyon says it's miles from the rendezvous point, they'll never have time to get back before the charges blow. Southern tells them they're wasting time and their lives are at stake, but Kenyon tells him maybe it's his life, not theirs.

The robot grabs Southern, causing him to drop his gun and the key. Dempsey gets the key and takes his bracelet off, then tosses the key to Kenyon. As Kenyon removes his bracelet, he tells Southern they're going to leave him here, but first, they'll take off his bracelet. They'll then fix the charges and clear out of here, then in three hours, this place will blow up with Southern still in it. Dempsey searches Southern and says he has no radio, but wonders if anyone is working with him. They could get in and rescue him. Kenyon says they'll shut the electronic doors and jam them, so nobody can get in in time to save Southern.

They put the charges down and leave. Southern says he may be finished, but so are they -they won't escape. Kenyon tells him to quit fooling himself, no one can stop them, least of all him! The first door is then shut, as Dempsey fires at the controls. The control panel for the door is broken.

Southern manages to pull out his radio pen, and uses it to contact his HQ. He says this is an emergency, as things have gone wrong. The fuses have been set and the nuclear store will explode at 1230 hours. There's no time to save him, as Dempsey and Kenyon have jammed the doors. He says the entire area must be evacuated. HQ says they've got less than three hours to do that, but Southern says once those fuses blow up they'll cause the biggest explosion the world has ever known. He says to forget him and save the thousands of people who are in danger, many of them can be saved if they work fast. Meanwhile, Kenyon and Dempsey continue to work their way out of the plant, sealing the doors and destroying the controls as they go. The finish the last door, so Kenyon says now they've got a long, fast drive south to meet the leader.

HQ tells Southern someone has come up with an idea to save him: International Rescue. Southern says of course, but perhaps they can stop the leader at the rendezvous spot. HQ isn't sure if International Rescue would do that, as they're strictly a rescue organization, not a police force. Sir William Fraser of the British Security Service then calls International Rescue, and John responds. He fills John in on the details. Near Tracy Island, Tin-Tin, Alan and Gordon are fishing, but then get a call from Jeff.

Jeff and Brains tell Scott and Virgil about what's going on, and the fact that they've got just two and one half hours. Virgil says he'll take pod 5, with the laser beam equipment. As he and Scott leave, Brains asks about the ones who started all this trouble. Jeff says it's not their job to catch crooks, no matter how dangerous they are. Brains says their agent in Britain could help, so Jeff contacts her. Penelope uses her teapot radio to listen to Jeff, who says foreign agents are fleeing Britain, and must be stopped. He gives her the location, and she says she'll do her best. She tells Parker to get the Rolls Royce.

At Tracy Island, Scott takes off in Thunderbird 1, followed by Virgil in Thunderbird 2. Penelope and Parker head out in FAB 1. Parker asks if they're going to be on time. Penelope says it'll be touch and go, as they can't afford any holdups.

Scott finds out Virgil's estimated time of arrival at the danger zone is 12:10, and he's flying at maximum speed now. Scott says that'll give them less than 20 minutes to get into the plutonium store. Meanwhile, Penelope asks Parker what the delay is. Parker says it's this truck in front that he can't get past. Penelope says they're behind time, and instructs Parker to use the horn. Parker is eventually able to get past the truck.

Scott tells Virgil he'll try to contact Southern. He lands Thunderbird 1 and gets through to Southern's radio frequency. He tells Southern that Thunderbird 2 will be here in five minutes, and they'll soon have him out. Southern advises him to get away whilst he can, as it's impossible to reach him in time. Scott says they've come a long way to get him out, and that's exactly what they're going to do. Southern tells him to get clear, but Scott says International Rescue doesn't give up that easy.

Virgil then arrives in Thunderbird 2. Thunderbird 2 lands and Virgil has it rise up, revealing pod 5. The pod door opens up, and Virgil drives out in the laser cutter vehicle. Scott says they'll have to work fast, as these doors are jammed tight. They can't blast their way in as the charges may upset the fuses, not to mention the plutonium. Virgil starts using the vehicle's laser beam.

The laser starts to cut through the first door. Scott says they've got 14 minutes until those fuses blow, and there are two more doors to get through after this one. Virgil finishes cutting through the first door. He then uses the vehicle's air jets to blast it down, letting them progress to the next one.

They drive up to the next door and start cutting through it. After a few minutes the door is cut, so Virgil hits it with a jet blast to knock it down. Meanwhile, Parker decides to take some short cuts to get to the location of the helijet, and takes FAB 1 through some fields.

The bracelets start to smoke. Virgil and Scott get to the last door with seven minutes to go. They cut through the door, and then blast it down. Scott says he'll get those fuses, and tells Virgil to take care of that robot. They now have just five minutes left.

Scott picks up the bracelets and runs back to Thunderbird 1. Virgil tells Southern they'll soon have him free, as he gets to work on deactivating the robot. Meanwhile, Scott gets back to Thunderbird 1. He takes off and flies over the sea.

After flying a short distance, he opens a hatch, causing the three bracelets to fall out and hit the water. They explode seconds later, so Scott radios his father that this is the last time the Erdman gang can try the bracelet game on anybody. Jeff says that's right, and guesses that Prescott is fully vindicated now. Scott says it only remains for Penelope to tidy up the details.

Kenyon and Dempsey have arrived at the place where the leader's helijet is, and are already inside it. Kenyon says he's glad things turned out the way they did, as it means they get a bigger share of the loot. The leader says all they have to do is escape to safety, which should be quite a simple matter. Just then, FAB 1 charges down a fence.

The helijet begins to ascend, but gets hit by a shot from FAB 1's cannon. FAB 1 fires a couple of more times, causing the helijet to crash back down on the ground and mostly explode.

Virgil tells Scott that Southern is in a bad way -if only he could have released him quicker. Scott tells him he did his best, and those robots aren't the easiest guys to handle. He says he'll call for an ambulance, as they'll have to get Southern to a a hospital. They then seen FAB 1 drive up. Penelope says she was successful with her mission. Scott introducers her to Southern, the agent they just rescued who needs hospitalization. Penelope says to get him in the car, she'll take him herself.

Sometime later, Southern is at Penelope's home. She asks him if he's fully recovered, and he says he's as fit as ever. But this is the end of his career as a secret agent. Penelope asks why, and he says his cover has been broken. Secret agents are only able to operate if they remain strictly incognito. But he guesses a person in Penelope's position wouldn't know that. Penelope says she wouldn't, but says it does sound fascinating. She's often wanted to do something exciting, like being a secret agent. Southern says it's not all romance, and in actual reality it's a tough existence, never being yourself. He thinks someone like Penelope, so sheltered and gentle, just wouldn't be her. With all due respect, she isn't the type. Secret agents walk with danger as a shadow, death is a constant companion. He thinks Penelope should just be what she is: a very beautiful lady.