Ocean Pioneer I sails the seas. It's transporting a shipment of the highly combustible liquid alsterene. On the bridge, Captain Johnson tells the Commander that six more ships like this one are going to be built, giving them the most modern fleet afloat. The Commander says that's if his line doesn't catch up to him, as his company want to cut the overheads by getting at least eight tankers just like this one as soon as possible. Johnson says that three men looking after 120,000 tons of sea-worthy steel certainly makes the balance sheet look good.

Collins then says that the reactor is overcompensating. Johnson tells him to switch to manual, he'll trim it. Collins does so and starts giving his reading, but the numbers keep rising. The Commander then says there seems to be quite a large amount of mist ahead. Johnson thinks it's strange.

He says that usually, the weather boys don't slip up on this kind of thing, but they didn't make any mention of mist in their weather report. Collins continues to report that his readings are still rising. The ship heads into the mist... and explodes moments later!

Sometime later, Penelope is at the christening of the Ocean Pioneer II. Lord Worden tells her that as chairman, the men certainly appreciate her doing them the honor today. Penelope says it's her pleasure. Nearby, Parker and another chauffeur called Stephens make a toast to Lady Penelope, and proceed to get even more drunk. Penelope says it gives her great pleasure to name this ship Ocean Pioneer The Second. She pulls down a lever, causing a bottle of champagne to fall.

It smashes on the boat. With the christening complete, Ocean Pioneer II then slides down into the sea. Penelope says how lovely this is, and how incredible it is how they can fit these ships before launching.

The christening is being covered by news crews, and the Tracy family watch it on TV. The reporter says that despite the day's excitement, there must be many who's thoughts turn to the ill-fated Ocean Pioneer I, which disappeared only six months ago. Penelope is then interviewed, and she talks about how great it all is, although she confesses the bottle didn't quite break with the pop she expected. Jeff says that all they've got to do now is wait for Penelope to report in.

Penelope goes back to FAB 1 and finds Parker sleeping. She wakes him up and asks if she can hear him. He says loud and clear, so she asks him where he got the champagne. Parker says 1998 was such a good year, it seemed a pity to waste it. So he switched the bottle earlier. Penelope thought that bubbly didn't hit the ship with much of a bang! She wants to know what it was she launched the ship with, and Parker reveals it was pure tonic water. Penelope says she'll have to talk about this later, she's got an urgent message to relay to Jeff.

Penelope contacts Tracy Island and says her plan to launch Ocean Pioneer II was highly successful. Jeff asks if anyone suspected anything. Penelope doesn't think so, and Lord Worden was only too delighted to have her on the platform. She did go over the ship, but found nothing that indicated sabotage. She really believes that the ship is in no danger. Jeff says he's glad he has her assurance, and thanks her for investigating it. As the call ends, Jeff says that despite what Penelope says, he's still worried about that craft. Scott and Virgil ask why he's worried. Jeff says that if Ocean Pioneer I can blow up in the middle of the ocean for no apparent reason, anything can make sense. He has a feeling they're going to hear more about that ship.

Tin-Tin says there's no use brooding over it, if anything's going to go wrong, their worrying over it won't prevent it. John then contacts them and says a distress call has come in from Oahu in the Pacific. A typhoon just hit the island and struck the hospital full force. The foundations are crumbling and the patients are in extreme danger. Jeff tells him to brief Scott once he's airborne, as this has got to be quick.

Scott heads off to Thunderbird 1, and takes off. Scott reports in and reports his course. John has told him that a tidal wave has undermined the footings of the main hospital on the island. Scott tells his father that they'll need Thunderbird 2 with double crew and pod 3. Jeff tells Virgil to be on his way with pod 3. As Alan is due in Thunderbird 5 soon, he tells Gordon to go with Virgil.

Thunderbird 2 is soon in the air. Scott report in again, saying he'll be at the landing zone in two minutes. But as he continues to talk, the picture breaks up and the audio keeps cutting in and out. Virgil then contacts them, but the interference prevents him from being heard as well. Jeff thinks this could be very serious.

Brains has a look and thinks that John in the satellite will be out of contact too. He thinks that this will only effect transmissions via the satellite. The last time it happened it cleared itself, but the interference seems to be much stronger this time. Jeff asks Alan if he can take off now, and Alan says he guesses so. He tells Brains to go with Alan, as they've got a complete communications blackout, and that leaves them vulnerable. Alan and Brains head off to Thunderbird 3, which then blasts off into space.

Thunderbird 3 docks with Thunderbird 5. Brains records the interference and has it put onto tape. Alan thinks its a mighty long way to come just to pick up a reel of tape, but Brains says that for analytical purposes, a recording made outside the Earth's atmosphere is much cleaner. John says they need to move, because as soon as he gets him back to the base, the sooner he can work on an answer.

Alan reminds John he owes him six hours. John and Brains board Thunderbird 3, which then leaves Thunderbird 5 and heads back to Tracy Island. At the island, Kyrano asks if there's no news yet. Jeff says they haven't heard a whisper, as that interference is still with them. He finds it terrifying how much they depend on communication in this rescue business.

Tin-Tin tells them they mustn't encourage one another, as this is probably nothing to worry about. Kyrano asks Jeff if he's heard from Brains, and Jeff says they haven't. With all this interference in the air, long-distance transmissions are out. As far as he knows, only transmissions over short distances are possible, such as between Thunderbirds 1 and 2. But they then hear the sound of Thunderbird 1, which is on the way back.

Scott lands Thunderbird 1 and then goes up to the lounge. He explains that they managed to shore up the walls with hydrostats, but not before the isolation ward collapsed. There were no casualties due to there being no cases in the ward at the time. Virgil and Gordon should be back soon, as they found they could contact each other when they were up close, despite the interference. As Scott heads off to get cleaned up, Tin-Tin reminds Jeff that the inter-telecast on Ocean Pioneer II is almost due.

Thunderbird 2 soon arrives back at the island, so Virgil lands it on the runway. Scott says that all they need is for Thunderbird 3 to get back, and the whole team is together again. Tin-Tin hopes Brains can clear up the mystery of the interference. Later on, Brains and Tin-Tin are in the lab. Tin-Tin plays the tape once more, and they hear the static noise.

Brains tells Tin-Tin to keep that sound in her mind, then listen to this. In the lounge, Jeff watches the report about Ocean Pioneer II. The reporter says that the ship has its first cargo of liquid alsterene, and now sails the blue waters of the Mediterranean. There are just three men, one ship and 200,000 tons of nature's latest aid to mankind: liquid alsterene. On the ship, Jensen reports to base and says everything is under control, all systems go.

The Captain tells his number two that they'll be at home and dry in no time at all. The ship continues on its journey. Back at Tracy Island, Brains asks to see Jeff in the lab. Jeff asks if there's trouble. Brains says they've traced the interference, but it presents a few problems. Jeff says he'll be right with him.

Brains tells Tin-Tin to set up again, but measure the quantities very carefully. Tin-Tin pours some liquid into a test tube, which is then transported into a chamber. Jeff enters the lab, and Brains tells him they're just setting up. The test tube arrives in the chamber, so Brains asks Tin-Tin to play the recording. They all hear the noise, and Brains tells Tin-Tin to turn the microphone on.

Brains says that their experiments show that the result of close proximity of a high density liquid fuel and a low density substance known as OD-60 produces high impedance waves, which can interrupt and cut off radio communication on their bandwidth for a given distance. Brains asks Tin-Tin to switch the microphone off. Jeff says that's the cause, now for the cure. Brains says the experiment is not quite finished, and tells him to observe the contents of the test tubes. By bringing them into even closer proximity, further chemical action takes place.

The test tubes get closer until they explode. Jeff asks what this all ads up to. Brains says it adds up to a very large explosion in whatever area one finds both A and B. He mentions that A is alsterene and sea fungi found close to the Gulf Stream: OD-60. He says that OD-60 is used to make dog food, of all things. Scott says he's got a fix, but it doesn't make sense: it's the middle of the Mediterranean, miles from the Gulf Stream and miles from the nearest landfall.

Jeff asks if OD-60 is only found in the Gulf Stream area. Brains believes so, but Tin-Tin says Penelope could soon tell them, as she was on the panel to judge the Allpets poodle competition. She recalls the Allpets slogan: the only dog food that uses the food nature provides from the sea. Jeff tells her to get into contact with Penelope right away, he wants to know each location of OD-60 and whether any has been found in or near the Mediterranean. He tells Scott he has a hunch there is a great pile of OD-60 here, and points out a place on the map. But it's more than a hunch that Ocean Pioneer II is sailing with 200,000 tons of alsterene.

On the ship, Jensen reports that they are 75 miles from the coast. He is then contacted by the base, so he reports the ship's position and current speed. But then the radio signal breaks up. Elsewhere, Penelope has gone to the Allpets building, where she meets Sir Arthur. She is happy he has seen her at such short notice, but this is all for a doggie book she's compiling. In the chapter on feeding, she feels her readers will want to know more about OD-60. Arthur knows he can rely on her digression, as he doesn't want everyone knowing where to trawl for their product. He has a poster move up, revealing a map behind it.

He says that if you follow the Gulf Stream from its source and around the coast of Florida, you'll find the main sources of OD-60. Penelope asks if there are other sources, but Arthur says they don't know yet. He tells her to look at the map, and the distance they have to transport OD-60. The capital costs are crippling to his company, so what they've done is put 150,000 tons of active OD-60 in the Mediterranean, in the hope it'll flourish and provide further raw material for Allpets. Penelope asks if this means there is OD-60 in the Mediterranean, but Arthur says they don't know for sure yet. Penelope promises not to tell any of the girls at the club -he can count on her.

Penelope leaves and goes back to FAB 1. Parker trusts the mission was successful, and she says it was. Sir Arthur has confirmed all their worst suspicions: there really is OD-60 in the Mediterranean, so she must radio Jeff at once -Ocean Pioneer II is heading straight for trouble. At Tracy Island, Scott tries to contact the crew of the ship, but can't get through to them. Jeff says it was just a long shot, and Virgil says it's no use waiting for them to send out a distress call -they aren't going to be able to make one.

Scott takes off in Thunderbird 1, whilst Virgil and John take off in Thunderbird 2. Out at sea, the crew of Ocean Pioneer II are still heading towards the OD-60, completely unaware of it being there. Jensen tries to contact the base, but says he still can't get through.

The Captain tells his Number Two to trim the reactor definition, as it's two points over. Number Two says it won't respond, so the Captain tells Jensen to switch to manual so he can trim the reactor himself. Jensen switches to manual, so the Captain tells him to read out the readings as he trims. Jensen starts calling out numbers, and says they keep rising. The ship's speed then starts getting higher.

The Captain says the reactor has gone too far and orders for the radiation shields to be closed down. He then orders for a course change and says what a maiden voyage this has turned out to be -even the weather is deteriorating! Up ahead, they see what appears to be thick fog. The radiation shields are then closed.

The boat continues to move forwards, and soon enters the fog. The ship's speed gets to 85 knots, and the Captain says the engine's won't be able to stand it. The engines being to shake and smoke, and the there is an explosion on the deck.

The ship's air con switches off, and the engines cut out, leaving the ship slowly moving through the fog. The Captain tells Jensen to try the radio and call International Rescue, as it's their last chance and they won't last long without air. Jensen tries to make the call.

Scott arrives on the scene in Thunderbird 1, and reports that the ship is drifting off course towards the danger zone. There's quite a lot of mist around, which isn't going to help. Virgil says he can hardly hear him, as the interference is really getting worse. He suggests they try to keep radio contact to the minimum, so Scott says he's going to try and land on the deck. Thunderbird 1 soon touches down on the ship.

Inside the bridge, Jensen is still trying to contact International Rescue. Scott walks up to the bridge and sees that the fog is getting real thick, so he hopes Virgil isn't far off. In Thunderbird 2, Virgil and John see all of the thick fog down below.

Scott places a device on one of the windows and tries to make contact with the crew inside the bridge. But he doesn't get a response from anyone. Virgil says they'll never find the tanker in this fog, and tells John to try to get through to Scott so they can home in on his signal. John tries the radio, but all he hears is static. Scott then briefly sees Thunderbird 2 and tries to call again. He gets through and says he can hear the motors, and gives directions to Virgil.

Virgil follows Scott's directions, and finds the ship. Virgil hovers Thunderbird 2 over Ocean Pioneer II and then has John lowered down onto it via a ladder. Scott tells Virgil that as soon as John hits the deck, stand well clear until he sends for him.

John arrives on the boat, so Thunderbird 2 moves away. He goes up to where Scott is, who has used a laser beam to cut through a door. He knocks the down down and sees that the crew are all unconscious. They are about to go inside, but then see how the water around the boat is bubbling. Scott says they must be right over the OD-60 now.

John tells Virgil he'd better come in and standby, and step on it or they might not be around when he gets here! Scott brings around the crew. The Captain weakly says they must call International Rescue, as it's their only hope. Scott sure hopes he's right. Outside, Thunderbird 2 arrives back at the boat, and starts to drop.

It accidentally hits a mast, but doesn't take any damage. Scott tells the Captain to lead his men off the ship. The Captain is about to thank him, but Scott says there's no time for that, the ship is about to blow up. The crew board Thunderbird 2, and as John gets on the ladder, Scott tells Virgil to pull away.

Thunderbird 2 moves away from the ship. Scott rushes back to Thunderbird 1, which begins to take off. But then, a series of explosions hit Ocean Pioneer II, which quickly sets off a chain reaction leading to the complete destruction of the ship.

John says there's no sign of Scott anywhere. Virgil keeps trying to contact Thunderbird 1, but gets no response. Virgil says the interference has cleared, but Scott doesn't answer. John thinks Scott has just got to have made it. Virgil tries the radio again, but this time Scott does respond, saying he's hearing him loud and clear. Thunderbird 1 emerges from the fog, and Scott says he'll see them back at the base. Once they get home, Scott and John discuss the rescue. John says that 120,000 tons of ship stands for a heck of a lot of capital investment, so they should have tried towing Ocean Pioneer II out. Scott says sure, but asks if he thinks they could have made it in time. John says who knows, but that's all part of the game.

Jeff tells them to hold it, and asks John how many rescues he's been on. John says about a dozen, so Jeff asks Scott the same question. Scott says he's been on all of them. Jeff says ok, but they still argue. John says they weren't arguing, whilst Scott says they were just discussing. Jeff tells them to listen: for many years now, man has worked to perfect the material things in this world, and has done pretty well for himself. If a building falls down, he can still build it up again. But life is different, which is why the objective of International Rescue will never change. Their job is to save lives that are in danger, and that's how it's always going to be.

Scott says that's ok by him, and John says sure. Jeff tells them to go and dip their hot heads in the pool, so he can read his book.