International Rescue's engineering genius Brains has invented the strongest metal compound known to mankind. The base of the metal's formula is Mozatinum, a rare mineral found beneath the ocean. Drilling for a new Atlantic tunnel offers the possibility of a fresh supply. Jeff Tracy contacts the tunnel authorities to register a claim, but he has a rival in one Mr. Shendon and his team of geologists. Brains and Alan Tracy are surveying the American end of the tunnel when a section collapses, leaving them trapped. But this is no mere accident, and the mysterious Mr. Shendon is not what he seems...
Near Tracy Island, Scott (aboard Thunderbird 1) and Gordon (aboard Thunderbird 4) are carrying out a test on Brains' latest invention. Thunderbird 1 launches a target, which Thunderbird 4 launches a missile at. However, the blast from the missile only flings the target aside, bareley damaging it. Once the test is complete, Scott and Gordon return to base.
The target (Brains' latest invention) is a missile, made out of the strongest metal compound ever known to mankind; however, according to Brains, the base of the metal's formula is the very rare mineral called mozatinum, which can only be excavated from beneath the Atlantic ocean bed, where the Atlantic Tunnel scheme is well underway. Also, Jeff Tracy must acquire permits for the excavation.
Meanwhile, Kyrano and his daughter Tin-Tin are out in the gardens attending to the orchard when Kyrano suffers a mysterious attack; this attack is carried out from within a Malaysian temple where Kyrano's half-brother, the Hood, is speaking to him via a statue. The Hood demands knowledge of International Rescue's upcoming project, and Kyrano explains about the mozatinum and the Atlantic Tunnel. The Hood decides to get himself a permit, and makes plan to pounce on International Rescue. Jeff and Tin-Tin find Kyrano, but strangely he feels alright; however, Tin-Tin knows that this isn't the first time that he suffered these "mysterious attacks".
Three months later, Jeff gets the survey permits for his own leased section of the Atlantic Tunnel, and he sends Brains and Alan off to Boston where the American end of the tunnel is located. Meanwhile, at an office block not far from Boston, Mr. Shendon tells Vincent Baker and his team of geologists about his expectations. But, as soon as they leave the office, it turns out that Mr. Shendon is actually the Hood in disguise; he's only interested in International Rescue's claim.
Upon arrival at Boston, Alan and Brains use a shuttle car to take them underground, where a man recognises Brains - Vincent Baker; five years ago, he and Brains used to be university students in England. Vincent explains that he's working for "Mr. Shendon" in Shaft K273, and Brains explains that he's working for Alan's father (their boss, in Brains' words) in Shaft K279. Before all of that, they examine the main tunnel excavations. Upon arrival at Shaft K279, Brains and Alan drive a shaft buggy up to the rock face, and Brains uses one of his own inventions: a metallurgy tracer beam. However, further analyst requires some rock samples, so they take some back up to the surface where they use the command laboratory.
Also in the lab, Vincent Baker asks his friend to check is rock sample which contains Uranium GS70, and then, he goes off to tell "Mr. Shendon", who wants to use explosives in order to shift more rock. However, Baker informs him that only the tunnel authorities are allowed to carry out the rock blasting, so therefore, an application is required. Once Baker leaves, the Hood removes his mask, explaining to himself that he doesn't wait for anyone. Inside the cafeteria, Brains tells Alan that Baker didn't realise that mozatinum was inside his rock sample, but as it's a rare metal, it's not very recognisable.
Later, Alan and Brains return to Shaft K279, unaware that the Hood is watching them; he wants to get hold of the very mineral that International Rescue need. So, upon returning to the surface, "Mr. Shendon" orders Baker to carry out the excavations at once. However, once again, Baker informs that the explosive experts must be required, and in return (once again), "Mr. Shendon" says that the authorities take far too long, but he eventually "agrees" and tells Baker and his colleagues to take a break.
However, that afternoon, the Hood sneaks into Shaft K273, and places some charges. Then, he sets them off, and then, he takes a rock sample back to the surface. But, the explosion causes major side effects; severing the light and power cables in Tunnels J, K, L and M; also, travels along weak stratas, causing a series of cave-ins, trapping Brains and Alan in the process. In total, thirty tunnels have collapsed.
Soon, the tunnel controllers report to the emergency services, which gets picked up aboard Thunderbird 5. John reports to Tracy Island, and soon Thunderbirds 1 and 2 are launched. Once at the Atlantic Ocean, Scott uses Thunderbird 1's sonar sounding equipment to locate Brains and Alan, and upon picking up the signal, relays instructions to Virgil. Also, Scott informs the control of the Atlantic Tunnel at Boston to keep the area clear for them apart from police and officials and their no photograph policy.
Soon, the Hood finds out that International Rescue are on their way, giving him another chance to steal their secrets. But, as he exits from the lab, the Hood gets caught out by two police officers who take his camera and orders him back inside. Meanwhile, Virgil lands Thunderbird 2, and unloads the Excadigger. Once inside the main shaft, the Excadigger clears away the huge boulders until he reaches the collapsed Shaft K279 where he finds Brains and Alan who unfortunately has a broken leg. Virgil tells Alan that he'll "inform" the tunnel authorities that he'll take him straight to hospital aboard Thunderbird 2.
Once back at Tracy Island, Brains tells Jeff that the rockfall was caused by an explosion, worrying him that more stradas may have being weakened; which indeed they are as, back at the Atlantic Tunnel, the main shaft gives way, trapping ten men with no air supply. The tunnel controllers call International Rescue back on the scene, and this time, Gordon goes with Virgil; Thunderbird 4 is required to get air down to the trapped men.
After launching Thunderbird 4 into the Atlantic Ocean, Thunderbird 2 continues on its way. Scott sets up mobile control at the Boston base of the Atlantic Tunnel, and Gordon uses a special drill to get air down to the trapped men. However, the trapped men all realise that the atomic reactor on the rock cutter is broken, now they'll be exposed to radiation exposure.
Just as Thunderbird 2 arrives and unloads the Mole, the Hood is making his next move. He makes a mask of the very police officer called Sweeney who took his camera earlier, and then, he knocks the real Sweeney out and steals his uniform. Then, sneaking behind Scott at the mobile control, the Hood shuts off the photo-alert. Meanwhile, Virgil (inside the Mole) comes across some granite, slowing him down. Back on the surface, the Hood in his disguise relieves the officer guarding Thunderbird 1, and starts taking pictures.
With Thunderbird 4 supplying air to the trapped men, and the Mole finally breaking through, there's only fifteen minutes left. Virgil quickly and carefully seals off the isotopes on the rock cutter, and then, he gets all ten men aboard the Mole. However, back on the surface, the Hood has completed his photography when he gets caught out by Sweeney who removes his mask from his face. But then, the Hood shoots Sweeney with a gun, and quickly makes his escape aboard his private aircraft.
Despite being wounded, Sweeney staggers to his feet calls out a warning just as Virgil comes out of the main shaft with the Mole, almost running him over. Sweeney explains that the Hood took a full photographic record of Thunderbird 1, so Virgil orders Scott to track him down. Taking off aboard Thunderbird 1, Scott soon finds the Hood aboard his aircraft. The Hood tries to shoot Thunderbird 1 down, but Scott reacts and shoots down the Hood's plane. The Hood ejects, but loses his camera in the process. Using a micro-missile, Scott destroys the Hood's camera, maintaining their secrecy. Meanwhile, Virgil informs Scott that the ten rescued men will recover within a fortnight according to the medics.
Once the Mole is back on aboard, Thunderbird 2 collects Gordon and Thunderbird 4. Then, Scott relays a message from the police to Virgil; the Hood got away again, but Sweeney is recovering in hospital. Back on Tracy Island, Jeff explains that he got permission to use Shaft K273 allowing Brains to get the mozatinum, whilst Alan is ready to relieve John in Thunderbird 5, knowing that his broken leg will recover aboard the space station.
(In order of appearance)
- Scott Tracy
- Jeff Tracy
- Alan Tracy
- Gordon Tracy
- Tin-Tin Kyrano
- The Hood
- Vincent Baker
- Vincent Baker's Colleagues (don't speak)
- Harry (Tunnel Controller)
- Unnamed Tunnel Controller
- John Tracy (mentioned)
- Sweeney (Police Guard)
- Unnamed Police Guard
- Ten Trapped Men (Unnamed)
- First appearance: The Excadigger, a Pod Vehicle used by International Rescue. It would go on to appear once again in the 1966 novel Ring Of Fire.