A gigantic vehicle called the Sidewinder makes its way through a jungle, ripping out any trees that get in the way. Nearby, a helicopter is following, and General Peters says to just look at that thing -it's like a monster from another planet. Lieutenant Ralph agrees, and says that nothing can stand in its way. The Sidewinder exits the jungle.

The Sidewinder crew -consisting of Colonel Sweeney, Frank and Johnny -contact the General. Sweeney says the jungle test is complete, and asks how the Sidewinder looked. Peters says it looked just fine, and that this wraps up the tests. The relief crew is on its way by helijet, so he tells them to take the Sidewinder to a certain point, and then the helijet will take them back to base.

Peters says that the Sidewinder is just what the army needs for these bush fire wars that keep springing up. Ralph hears over the radio that the relief crew is heading to the rendezvous point, so he tells their pilot to take them back to base. As they head away, the Sidewinder starts to move forwards. Sweeney says he can't wait to get back to base, and Frank agrees. He thinks that three weeks in this tin can isn't exactly his idea of heaven.

As the Sidewinder walks, the ground it stomps on begins to crumble and break away. Suddenly, the ground opens up beneath it. The Sidewinder suddenly falls and rolls down into a deep pit, starting a fire and causing large amounts of smoke to rise up.

Peters tries to contact the Sidewinder, but gets no response. They then see the smoke, and realize that the Sidewinder has disappeared. They head towards it, but can't see much due to all of the smoke. But they then see the giant hole in the ground. Peters tries to contact the Sidewinder crew again.

They then get contacted by the relief crew, who say they're at the rendezvous point, but there's no sign of the Sidewinder. Peters says there has been some trouble, and tells them to come to where they are. Peters then tries to contact the Sidewinder crew again, but this time gets a response. The crew have all survived, and Sweeney says despite a few bruises, they're still all in one piece. Peters asks how it looks down there, and Sweeney says the Sidewinder has tipped over onto its side, so it can't move. He also finds out that they're 300 feet down.

Peters wonders what they can do. Ralph says that the Sidewinder weighs upwards of 500 tons, so they'd need some pretty heavy lifting gear. Peters says this is the middle of the wilderness, it'd take weeks to get equipment out here. Their pilot then says he'll have to move their helicopter away from the pit, as the heat from it is building up. If they remain hovering here, they'll be needing a rescue team themselves. He lands the helicopter near the pit, just as the helijet arrives.

Sweeney wants to know how they got down here. Frank thinks the ground just opened and swallowed them. Sweeney wonders how they're going to get out, as the whole pit seems to be on fire. Frank says they'll be ok for a while, as the automatic cooling plant switched itself on. Sweeney says that the atomic reactor was due for refueling, so it won't hold out forever. Outside, Peters explains what's happened to Mead and Reynolds, the relief crew. Mead suggests hauling it out, but Peters says no lifting equipment could reach here for two weeks at the minimum. Mead asks if they could use the helicopter and helijet.

Reynolds says the first thing they should do is go down there and take a look. Peters thinks that's be suicide, as the pit is an inferno. Mead thinks one of the copters could lower him down on a line just long enough for him to assess the situation. Peters thinks that's too dangerous, and he could be burned alive. Mead says if they don't do something soon, they'll be no could be for the Sidewinder crew. Frank says that the atomic reactor is operating at normal, and Sweeney hopes it stays that way. They are then contacted by Mead, who tells them he's going to attempt reconnaissance. He asks what the temperature is down there, and Sweeney says it's 220 degrees fahrenheit. He tells Mead not to try it.

Peters says they'll have to listen carefully, as Mead won't get much time to talk. Charlie, the helijet's pilot, takes off, and has Mead connected to the craft's winch. Mead is lowered into the pit.

In Thunderbird 5, John listens into the communications. He can hear Mead say that the pit is a real inferno, and that the Sidewinder guys are in some danger. John contacts Tracy Island, and tells Jeff that one of the army's new Sidewinders seems to have fallen into some kind of underground fire. One of the officers has gone down to take a look, and he transfers the communication frequency through to Tracy Island. Jeff, Scott and Virgil hear Mead, who says he's now 100 feet down, but can't see a thing due to the thick smoke.

He says that the temperature is rising, but tells Charlie to let go more line. He gets over 220 feet down, and keeps going. As he reaches 270 feet, he says his blood seems to be boiling. He says that the smoke is too thick, so he's going to have to go down all the way. He tells Charlie he'll only have a second, so he needs to be ready. Charlie says here they go, and he lowers the line even more.

Mead is lowered all the way, and he can see the Sidewinder. He then yells for Charlie to get him up, and starts screaming. He is taken out of the pit. Meanwhile, Jeff says this radio frequency should be put on priority monitoring, as this situation could get pretty desperate. Scott wants to shoot out there, but Jeff says no. They can't go shoving their noses into this uninvited, as for all they know the army might be engaged in a top secret operation. He tells John to keep this frequency clear, and then tells Scott to get Thunderbird 1 ready for launch. If the army decides they do want their help, they don't want to keep them waiting a minute longer than necessary.

At the pit, Mead has been wrapped up in bandages. Peters tells him he's in a bad way, but Mead says he'll be ok. He then says they could do it, they need to get a line attached and then haul the Sidewinder upright. Ralph says he's going to go down to fix that line to the Sidewinder.

Reynolds tells Ralph that this isn't his kind of job. He thinks the Lieutenant is a technical man, but this is a question of a man best equipped to succeed. Inside the Sidewinder, Sweeney finds out that the reactor is down by 20 points. He says the cooling plant is under-strength, so it means it's going to be warming up in here from now on. They're then contacted by Reynolds, who tells them he's coming down with a line he intends to slip over one of the Sidewinder's legs. If he makes it, they may be able to haul them upright. Sweeney thinks they may be able to climb out of here. The helijet then moves over the pit again.

Reynolds is then lowered down, and holds onto a line. He is quickly lowered 300 feet down, and Peters asks him if he can reach the Sidewinder. Reynolds says he doesn't know, as he can't see much. He asks Charlie to move the helijet over straight ahead, slow and easy.

Reynolds is moved over, and he can see the Sidewinder. He manages to put the line over one of the Sidewinder's legs, but then yells to be pulled up.

He is winched out of the pit. Peters tells Charlie to drop the line as close to them as they can, then get Reynolds and Mead to the base hospital. Charlie drops the line near the General's helicopter, so Peters tells Ralph to fix the cable to the copter. The helijet then flies off.

Peters tells Charlie to go with all speed. He then tells their pilot to get moving, as they've got to get the Sidewinder off its side. Their helicopter takes off, and starts to fly away from the pit. The Sidewinder starts to move, but its large weight is too much for the helicopter.

The line eventually comes off the Sidewinder's leg. Peters notices this, and Ralph asks if they made it or not. The Sidewinder tumbles back over onto its side.

Peters asks the crew what their position is, and Sweeney says they're back on their side again. Ralph says there's only one thing left to do: he'll go down there and try again. Peters doesn't like it, as two brave men have been badly injured in that pit, he doesn't know if he should risk another life. Ralph says they must keep trying, but Peters wishes they weren't so far from civilization, that way they'd stand a remote chance of effecting a rescue. Ralph hears the word "rescue" and says that's the answer. They then call International Rescue and explain what the situation is.

John tells his father that the army does want their help. Jeff tells him to tell them that they're on their way, and then tells Scott it's action stations -Thunders are go! Scott takes off in Thunderbird 1 immediately. Later on, Peters is concerned they still haven't heard anything from International Rescue, but Ralph says he's sure they're doing their best. Peters guesses they are, but he's worried about the Sidewinder crew.

Scott contacts Thunderbird 5, and asks John if he has any more information. John says that the Sidewinder fell into a crater some 300 feet in depth, and the pit is a blazing inferno. The machine weighs some 500 tons, and is on its side, meaning it can't move. The origin of the crater is unknown. Scott realizes they'll need the heavy gear, and since they don't know much about the crater, Brains had better come along. He contacts Tracy Island and says they'll need Thunderbird 2, carrying pod 5. They'll also need Brains, so Jeff tells Virgil and Brains to head out in Thunderbird 2.

Virgil boards Thunderbird 2, and selects pod 5. As Brains boards Thunderbird 2, Virgil moves his craft out onto the runway, and takes off.

Johnny says he checked the cooling plant a minute ago, and it'll only hold out for a couple more hours. Sweeney wonders how long the hull will stand up to that outside heat. Scott then contacts the army, and says he will be with them in four minutes. Peters tells him that the heat from that crater is fantastic, so they're going to find it tough going.

The Sidewinder crew then see that some smoke is getting in, and realize that part of the hull has cracked. Sweeney says to start the air purifier, and try to plug some of the fractures. Meanwhile, Scott lands Thunderbird 1 near the General's helicopter. Scott asks if there is any news from the trapped men, and Peters says that no -their radio failed ten minutes ago.

Sweeney asks if the air purifying system could be increased, but Frank says the exhaust fan is at full power. Sweeney asks how Johnny is going with those cracks. Johnny says these soaked rags are helping, but the heat is terrific on the hull. Sweeney tells them to keep at it, as they've got to hold on.

Scott asks how long the Sidewinder crew can hold out. Peters says they won't last for more than another two hours. Scott explains that other members of their organization will be arriving soon with heavy rescue equipment, but meanwhile he'll setup a remote TV camera so they can take a look at what's going on down there. Virgil then contacts Scott and asks how it looks. Scott says that he's about to deploy the camera, and does so from Thunderbird 1.

Peters warns that the camera will burn up, but Scott explains it's ok -this camera is specially constructed to withstand extreme heat. The camera enters the pit and descends, and Scott can see what it sees from within Thunderbird 1. Thunderbird 2 then lands next to Thunderbird 1. Scott tells Virgil that he's on his way over.

Inside the Sidewinder, the cracks on the hull are getting worse, and the rags are catching fire. Johnny keeps trying to put the fires out but says it's hopeless, as soon as the rags dry out they catch fire again. Sweeney says at least it stops some of the smoke. Outside, Peters wonders what's taking International Rescue so long, it's about time they had some action from them! Ralph says they must be doing their best, as it's a tough thing they're asking them to do.

In pod 5, Scott, Virgil and Brains look at the footage the camera is displaying. They see a piece of metal with the words "US ARMY" on it, and Brains says that's it. He thinks that way back in the past, this must have been an open-cast mine. When it was exhausted, a large crater would have been left. Virgil says it must have been used as a dump for military equipment after the Second World War, which explains the army wreckage.

Scott says he still doesn't get it, so Brains shows him a diagram he's drawn. The pit was filled in, and over the years a new crust of topsoil has formed. Spontaneous combustion caused a slow, smoldering fire which consumed the dumped equipment. The weight of the Sidewinder caused the thin crust of topsoil to collapse at its weakest point. Brains believes they need to remove the remainder of the crust so the Sidewinder can be dragged up the side of the pit. A little later on, Virgil has donned a protective suit, and gets the General's helicopter to lower him into the pit.

He reaches the bottom, but the smoke is so dense he can't see the Sidewinder. He tells Scott that it's like the inside of a blast furnace down here, and then says he'll start laying down the charges. Scott contacts the General and tells him to get clear of the smoke. Peters asks how they intend to get Virgil out of there. Brains says they have a machine called the Mole, which Scott is about to operate.

Out of pod 5 comes the Mole. Scott says he's heading to the drilling position. Frank says that the cooling plant has eight minutes in reserve, but then says that he can't breathe. Virgil contacts Scott and tells him that he's got one more charge to lay down.

Scott says he'll be with him in a few minutes. He then has the Mole rise upwards and start drilling down into the ground. Scott contacts Brains and tells him the angle he's drilling at. Brains says he's tracking him, and starts giving him coordinate adjustments to make as the Mole continues to drill.

The Mole starts rocking, and Scott says he's come up against an obstruction. Brains says it's hard-core granite, and gives Scott the relevant coordinates to make a detour. Virgil says the final charge has been laid, just as the Mole pierces through the other side of the crater. Virgil boards it.

The Mole withdraws back upwards, and reaches the surface. Scott tells Brains that they're clear of the area, so he can go ahead. Brains detonates the charges, which causes a series of explosions in the pit.

As the Sidewinder starts shaking, Sweeney asks what they're trying to do -blow them out of here? Peters asks what the hold up is, as his men down there have less than two minutes left. Brains tells him they're doing the best they can, and then contacts Virgil and asks him if he's in position.

Virgil drives out of pod 5 in the first of two recovery vehicles -the first operated by him, the second is remote controlled. The two recovery vehicles stop at the edge of the pit, and Virgil says he's ready to fire the magnetic lines.

Brains tells him what to target on the Sidewinder. The recovery vehicles take aim, and fire off two electro-magnets each.

Virgil says that the electro-magnets are in position, and then gets the recovery vehicles to move back. The Sidewinder starts to move, something the crew realize.

However, the remote control recovery vehicle starts to skid. The two recovery vehicles keep pulling, but then one of the electro-magnets falls off. Virgil says he'll have to wind it in and fire again.

The line is retrieved, and then fired at the Sidewinder again. It attaches, and the two recovery vehicles resume pulling. The Sidewinder is pulled over, and is dragged up the side of the pit.

The recovery vehicles keep pulling, and eventually the Sidewinder is completely pulled out of the pit.

Later on, the Sidewinder crew are onboard a helicopter. Sweeney sees Scott and thinks he must be the guy who hauled them out of the pit. Scott says he's one of them, the others are about to leave. Sweeney says they saved their lives, but Scott says to forget it -he's glad they could help. Sweeney tells him thanks. Virgil then contacts Scott, and says he'll see him back at base. Thunderbird 2 then takes off.

The helicopter with the Sidewinder crew in it then also takes off. Peters tells Scott that the Sidewinder has been saved, and there were no casualties. He asks what he can do to thank International Rescue, but Scott says it's all part of the service. But if he wants to help, he just needs to make sure no one tracks their aircraft. It's vital that International Rescue's operation stays a closely guarded secret. Peters says that's the least they can do, and thanks him again. Peters wishes he could have the International Rescue guys in his force, as Thunderbird 1 takes off and heads back home.