A pilot is told to proceed with an attack on an installation. The pilot is in a new type of jet, which is capable of flying at very high speeds. The pilot quickly blows apart the installation with a few missiles, and then also destroys a boat.

General Bron tells the pilot to return to base. The Hood has been watching, and Bron asks him if he's convinced now. The Hood says he's beside himself in admiration, this is the most vicious weapon he's ever seen! Bron says that with such an aircraft, he could be master of the land and sea as well, if it were not for Red Arrow. The Hood asks what the Red Arrow is, as surely no aircraft is superior to what has just been shown?

Bron says in speed alone the Red Arrow can outmaneuver them. He wants the Hood to do something for him, a little favor for which he'll repay him generously. He's tired of competition, his army is becoming impatient and restless and all rivals must be removed from his path. He tells the Hood that all prototypes of Red Arrow will be destroyed. The first test will be carried out soon, and it must fail. The Hood says to leave it to him -the Red Arrow is doomed!

At London Airport, Norman orders all personnel to clear test area 20. He wants all airport activity to be kept to an absolute minimum, and orders all emergency personnel to proceed to security stations M, P and Q. The countdown for Red Arrow project is now operating, and he tells everyone this is their final clearance. He tells Colonel Tim Casey that the test can proceed, and he's handing over the airfield control to him. Casey tells the Lieutenant to clear the hangar and get him the pilot. Outside, a hangar opens up, revealing Red Arrow 1.

Casey contacts the pilot, Race, and tells him to pay close attention to what he's going to say. This is no normal airplane he'll be taking up today, so he needs to remember that -no exhibition flying. Casey says he wants all flying instructions carried out to the letter and no more. He then tells Race to take off and climb to 6,000 feet. Nearby, the Hood parks his van in a parking space and says this is as good a place as any to watch the Red Arrow... he doesn't think it'll be going very far today. Back at the hangar, Red Arrow 1 is ready to launch.

Casey reminds Race to do things to the letter. Race says he understands, and Red Arrow 1 then takes off. As the people in the control tower watch, Norman tells Casey that's some aircraft he's got there.

Race contacts them and says all systems go. His altitude is 6,000, and his air speed 4,000. He reports his fuel level, but then says that his air speed is increasing. Casey tells him to hold his air speed below 4,000. Race says the air speed control reaction is negative, it's still increasing! Race tells him he must cut his air speed. Race says he can't hold her, he's being pulled off course!

Red Arrow 1 suddenly turns around, and heads back the way it came. Race says the cabin pressure is dropping. The Hood is watching the plane, and says this is excellent -it's working even better than he dared hoped it would! Race blacks out, as Red Arrow 1 goes into a dive.

The Lieutenant says he thinks Race has blacked out, so Norman says to sound red alert. Casey tells Race to bail out, but gets no response. The airport's emergency services are dispatched, just in time to see Red Arrow 1 crash into another hangar and explode.

The Hood starts his van back up, and drives off. Casey wonders what went wrong. News of the crash soon hits the press, and at Tracy Island, Jeff has a newspaper about it. The paper states that Colonel Casey is to be replaced. Jeff says the crash occurred during a series of tests on the Red Arrow.

It also states that Colonel Tim Casey said in spite of the crash, testing would continue, though he would no longer be supervising the operation. Scott asks if this is the same Tim Casey who was with his father in the early days of space travel. Jeff says that's right, but it looks like Tim has quite a problem on his hands. Scott thinks they should be able to eliminate all faults before a takeoff was attempted. Jeff reminds him that Red Arrow is powered by twin rockets, and that's still a pretty new field. But it's not like Tim Casey to test a new project and make a slip, so it could have been sabotage. The Red Arrow is a mighty powerful weapon, and some people would like to see it out of action for a long time.

Bron is at the Hood's temple. He congratulates the Hood on the feast, and says the fate that befell the Red Arrow was most gratifying. He says the Hood has served him well, so the Hood says services merit rewards. Bron opens up a casket full of jewels, but then slams it shut before the Hood can take anything from it. He says that soon, Red Arrow 2 goes out on test, and it too must fail! The Hood says it will. Bron says when the entire Red Arrow project is abandoned, the casket will be his. He tells the Hood not to fail him, and the Hood says he won't -the gold will be his.

Back at the island, Brains and Alan see something is approaching the island. It's moving fast, but is still a fair distance away. Brains thinks maybe it isn't coming here, it could maybe be heading for the Island of Moila. In the lounge, Jeff says those early Moon shots with Tim Casey sure were exciting. Scott asks if Casey knows anything about the International Rescue setup, but Jeff says of course not. They know the policy for their organization, and besides, Casey is part of the armed forces. They then find out that something is approaching the island.

Jeff says he doesn't think they were expecting visitors, unless it's some more of Tin-Tin's admirers. He contacts Brains and asks for a reading. Brains tells him there's an unidentified object approaching on high altitude flight path 408. Jeff tells him to keep tabs on it. Scott says path 408 isn't a commercial flight path, and Jeff says it's quite unusual.

Virgil asks what they're going to do, but Jeff says as long as their base remains undiscovered it's unlikely anyone will attack the island. There is one thing they should do: operation cover up. Jeff presses a button which changes all the pictures of his sons. Brains then says that this aircraft isn't calling at the Island of Moila, it's heading straight for their base!

Jeff, Scott and Virgil head outside, and see the plane. They realize that it's diving straight at them -Scott says they're being attacked! Inside the plane are two people, and the pilot hits a switch on the plane's weapon console.

A panel on the back of the plane opens up, and something drops out. But it's not a weapon, it's a message. When Jeff sees it, he says this has got to be Tim Casey, it couldn't be anyone else. He tells Scott and Virgil that it looks like they've got a visitor.

At a television relay tower in England, the Hood is busy setting up a device at the bottom of the structure. He finishes up and then switches it on.

He then contacts the staff in the tower. which is operated by two guys: Jim and Stan. The Hood says he is the relief maintenance, and he's checked the cross stanchion at 200 feet, so they shouldn't have a thing to worry about in tomorrow's storm. Jim thanks him for checking it out at such short notice. The Hood says not to mention it, he's glad to help them out. As he ends the call, he says now all he has to do is wait for the next test of Red Arrow.

At Tracy Island, Jeff asks Tim if he's still worried about tomorrow's test. Tim says he keeps remembering the last test. Every component was checked and double checked, Red Arrow 1 should never have crashed. Brains then comes over and says he's been over all the blueprints of Red Arrow, but can find nothing to fault. Tim says he was sure Red Arrow was sound, she should never have crashed.

Jeff says it looks like it was a case of sabotage after all. Brains says his theory is the aircraft was sabotaged by some sort of homing device that the pilot was unaware of. Tim says that would be one way of slipping through security. Brains says he's rigged up a small detector which could tell the pilot whether the plane was being diverted during the next test. Tim thanks him for his help, and says he'll send Goddard back to the base. Later on, Tim thanks Goddard for the ride, and tells him good luck with the test -but is sorry he won't be there.

Goddard says he's sorry too. Tim tells him not to forget to watch the diversion detector Brains gave him. Goddard says he hopes they've got the saboteurs licked now, as he looks at the diversion detector that's in the cockpit with him. He then takes off and leaves Tracy Island.

At the relay tower, Jim says it's just as well they got that stanchion fixed, as sitting above this lot, they'll wave about like a palm tree in a monsoon. Stan checks ones of the scanners, which is dropping. Jim says this means the storm has reached Iceland already. Stan says it looks like they're in for a swinging time.

At London Airport, the same hanger opens up again, revealing Red Arrow 2. Norman tells the Lieutenant that if he had his way, Colonel Casey would be here as well today. He just hopes they can clear up the mystery of Red Arrow 1 as soon as possible. He then contacts Goddard and tells him good luck. Goddard takes off in Red Arrow 2.

Goddard reports all systems are go, so Norman tells him to keep it steady. At the relay tower, Jim tells Stan to look at this, and points out a computer which reads the storm's cyclonic force. The indicator is going crazy, and Jim asks if it could be caused by the storm. Stan doubts it, but asks what could be causing it. He thinks there must be an aircraft in the vicinity, but Jim thinks there can't be, there's no flight path for miles around here.

Goddard reports that he's veering off course, this plane is flying itself! Norman tells him this is the same trouble as before, and he's already 80 miles off his flight path. As he's over open country, Norman orders him to dip the plane's nose to a crash position and then eject. Goddard looks at the diversion detector, then puts the plane into a dive and ejects.

At the tower Stan checks the relays and thinks it could be all this static flying about. But they're then contacted by Norman, who tells them that there is an unmanned aircraft in their vicinity. He advises them to evacuate sky control. Jim thinks he must be crazy, and tells Stan it's probably a million to one chance they'd get hit.

Stan says they wouldn't have been told to evacuate sky control unless they were in real danger, so he'd better get that elevator up here quick. Jim calls the elevator, which starts to move up to the top of the tower. Norman then contacts them again, telling them that the plane is on a collision course with their tower.

Inside the Red Arrow 2, the diversion detector displays that the plane is being diverted. Norman says this is incredible, he can't believe it. Whatever it is that's drawing the Red Arrow off course must have fantastic power. The Lieutenant says Goddard has landed safely, so Norman says to get him up here right away. Meanwhile, Red Arrow 2 continues to dive.

Stan tells Jim to listen -that plane is coming straight for them! He wants to know where that elevator is, but Jim says it's too late -here she comes! Red Arrow 2 them smashes into the relay tower.

The wreckage of Red Arrow 2 falls to the bottom of the tower, and explodes. The tower remains standing, but its structure has been heavily damaged near the top. Both Jim and Stan have survived, but Jim says it looks like they got hit pretty badly. Stan says this place is going to go over any minute, but they're trapped.

At London Airport, Norman asks Goddard if he's absolutely certain. Goddard says he is, the diversion detector was registering definite interference. Norman only hopes it gets accepted as evidence at the enquiry. The Lieutenant then says that it looks like the Red Arrow has hit the television relay station, as radio contact with the men inside it has been severed. Norman asks what they can do, they'll never get them out of there as a helicopter would be out of the question with that storm raging.

Stan gets over to the radio and says he's going to try and fix it. Maybe they can get through to International Rescue, as if anyone can help them, they can. Jim wonders what International Rescue can do for them in a storm like this. At Tracy Island, Tin-Tin tells Alan and Scott she doesn't know where they get their energy. Alan says they've just finished an exhausting game of checkers.

Scott says they're conserving their energy for that walk around the island they'd promised the Colonel for this evening. They then notice John's portrait flashing. Outside, Tim tells Jeff this is some place he's got here, but there's just one thing that baffles him. He can't figure out what they do with themselves all the time! Those boys of his ought to have something to occupy themselves with.

Jeff thinks he's right, but then notices the stirrer in his drink flashing. He excuses himself and heads off to the lounge. In the lounge, Alan thinks this would have to happen when they have a visitor at the island. Tin-Tin thinks they could trust Colonel Casey.

Scott says that's not the point, they've got to remain a secret organization. Jeff then comes in and asks what's up. Scott explains about the emergency call, and there's bad news for Colonel Casey: the Red Arrow has been sabotaged again! It has crashed into a relay tower and there are two men trapped at the top. Alan says the awful rescue conditions means a conventional rescue would be impossible. Jeff says he won't enjoy having to tell Tim about this, but first, they need to get out there and save those men. He tells Scott to head off, and tells Alan to get Virgil and bring him up here. He then tells Tin-Tin she must get Tim Casey out of the way, he doesn't care how she does it as long as he doesn't see what they're doing. Tin-Tin heads off.

Virgil arrives and Jeff explains what's happened. He says that Tin-Tin is going to give him a signal when everything's all clear and the Colonel is out of the way. Scott boards Thunderbird 1 and gets it ready for take off, but has to wait. Meanwhile, Virgil and Alan board Thunderbird 2 and select pod 3. They wait in the hangar.

Outside, Tin-Tin tells Tim that they've just heard there's a water mamba in the area. It's a rare tropical mammal, he may never get another chance to see one. Tim says he's an airman, not a frogman, but Tin-Tin then exclaims there it is, and dives. Tim tells her to wait, and dives after her. Tin-Tin then contacts Jeff and tells him that she's taking the Colonel down to the underwater cave.

She tells him to give her a call once they boys come back. Jeff tells her good work, and then tells Scott he's clear to go. Thunderbird 1 blasts off moments later, quickly followed by Thunderbird 2.

Virgil then contacts Scott. Scott says he's been in contact with the danger zone, and the area has been cleared for them. But the local conditions have been reported to be very bad. It must be tough at the top of that tower right now. At the tower, the top part of it continues to swing around.

Jim and Stan get thrown around. Thunderbird 1 soon arrives on the scene, and lands near the tower. Scott says there's no place here to setup a control center, so he'll operate from Thunderbird 1. Virgil tells him they'll arrive in 4.5 minutes, so Scott says to channel in the remote camera. Scott then sends the remote camera out from Thunderbird 1.

The remote camera inspects the structure of the tower, and the footage is fed back to Thunderbirds 1 and 2. Alan says the main stanchion is nearly gone. Scott tells Virgil this site is pretty dangerous, so when he comes in, he needs to land on the west side, away from the impact area. Scott then has the camera move higher up, where it's seen by Jim and Stan.

Jim wonders what they heck that is, and Stan says he doesn't know, but it means someone is down below. Thunderbird 2 arrives and lands, and Scott tells Virgil the tower isn't going to last much longer. Thunderbird 2 raises up, and the pod door opens. Alan drives the Booster Mortar out of it.

Alan says the Booster Mortar is in position, and asks Scott if he can angle them onto the platform. Scott says he'll get the camera up there, but they need to make this as quick as possible. Stan says the steelwork isn't going to last much longer, and Jim says International Rescue or whoever they are better hurry up, or they'll be down there beside them -in bits.

Alan angles the mortar, and Virgil checks it. Alan tells Scott to pull in the remote camera. Jim and Stan notice the camera moving away, and Stan wonders if it's too rough out there to attempt a rescue. Jim thinks they can't just leave them them up here, they have to try something to get them down! Alan then fires the Booster Mortar.

It fires a canister, which breaks through one of the tower's windows. Stan opens it up and finds some equipment inside it. He tells Jim to put this on before it's too late. As they're doing this, the tower continues to fall apart.

Stan opens a window, and tells Jim to go first. Jim climbs out and pulls a pin on his harness, which shoots him up into the air. Stan then climbs out and does the same thing, just as the tower's steelwork twists itself apart and collapses.

The tower falls down, and the control room smashes into the ground. Scott says those poor guys were just seconds too late, and Virgil says this is the first time International Rescue has failed. But Alan says to look -the men are alive! They see that Jim and Stan are floating down nearby.

The two land in a field. Virgil then notices something at the bottom of the tower. At Tracy Island, Jeff wishes there was something they could do to vindicate Tim Casey, and hopes that this relay tower crash will bring something to light. Brains asks how the operation is going, but Jeff says he doesn't like to pester the boys with needless radio calls when they're in the midst of a rescue.

Virgil then contacts his father, who says they've managed to save the two relay operators. But they've just found something that may have account for the disaster, and thinks him or Brains might have some ideas. He puts through the footage on the other channel, displaying the device found at the bottom of the tower. Brains says he thinks they have the solution, as this device would account for the Red Arrow going off course during testing.

Jeff tells Virgil to tell the police that the saboteur is most likely in the area of the relay tower. Meanwhile, the Hood is racing away in his van. He says that at last the Red Arrow has been destroyed, and in a few short hours the gold will be his. As he continues to drive fast, he happens to pass a police car, which puts it siren on and starts chasing after him.

The Hood says the police will never catch up with him. The police officers report they're going after a van, and another officer radios that they'll intercept at Ridgeway Crossroads. There is a diversion at the crossroads, but as soon as the Hood sees it he thinks it's an ambush. But he says they can't stop him now, so he drives right through it.

The Hood then contacts Bron and tells him that some evidence must have been discovered at the relay tower, and now International Rescue have sent the police after him. Bron calls him a fool, doesn't he know that you can never get away from International Rescue? The Hood says he's already managed to shake off the police. At the diversion, an officer tells the others they tried to warn the guy in the van that the bridge was down, but he deliberately drove through. Meanwhile, the Hood gets to the bridge, and drives right off it.

The van lands in the river below. The Hood has survived, but Bron has heard the bang and asks what that was. Not only has the Hood let International Rescue ruin his plans, he's proven he cannot even drive a car! He tells him he must fend for himself now.

Thunderbird 1 arrives back at Tracy Island, and lands. In the underwater cave, Tim asks if the water mambas live down here. Tin-Tin says she thinks so, although she hasn't seen one for a long time -maybe they've moved on again. Back outside, Thunderbird 2 returns to the island, and lands. It goes back inside its hangar.

Tim tells Tin-Tin she's shown him over 20 underwater caves and they haven't seen a mamba yet. He thinks if any of them had been around today, they'd have seen one by now. Tin-Tin starts telling him he just must see one, but then a light starts flashing on her swim cap. She tells him perhaps they ought to get back. In the lounge, Jeff has operation cover up put back on, and says everything must be exactly as it was before the rescue operation.

Tim and Tin-Tin return. Jeff tells Tim they've been looking for him everywhere, as they've just heard on the newscast that the Red Arrow sabotage case has been split wide open. Tim says that's great news, and asks who he has to thank for that. Virgil says International Rescue, who've found that Red Arrow was being drawn off course by a homing device placed by saboteurs. Tim says that's what he calls real enterprising, and he bets they sometimes wish they belonged to on organization like that.

Alan says he's right, it would give them something to occupy themselves with, as nothing ever happens around here. Jeff tells Tim they also want him back to the research base at once for reinstatement. Tim tells Tin-Tin things were sure happening when they were out swimming. Tin-Tin says they certainly were.

Later on, Jeff and Tin-Tin watch as Goddard and Tim take off. As the jet leaves the island, it deploys another message, this time thanking Jeff.