At a dock in Monte Carlo, a diver called Carl climbs onboard a boat. He finds a single man on it: Blacker. Without asking any questions or revealing himself, Carl shoots Blacker, killing him. He then starts frantically searching through several drawers until he finds a torch. He unscrews the battery compartment and finds what he was looking for: some papers which were rolled up and hidden inside a smaller canister. He takes the papers and the canister they were hidden in.

He then jumps off the boat and reenters the water. He attaches a bomb to the side of the boat before swimming away. As he does this, another boat approaches with two men in it: Tesland and Bondson. Bondson tells Tesland to move up alongside Blacker's boat. Their boat continues to move forwards.

But Blacker's boat then explodes. Tesland and Blacker watch as it sinks. Tesland thinks it could have been the fuel tanks, as that boat was petrol driven. Bondson says there is no sign of Blacker, so he'll have to go down there and look for him as he could be trapped. He needs to get those papers.

Blacker puts a diving suit on. Tesland tells him he'll have to work fast, before the local police get out here. Bondson tells him to stall the police, as he doesn't want the boat wreck touched. He then jumps into the water and swims down to the wreckage of Blacker's boat. He enters it and tells Tesland that Blacker is dead. He moves a filing cabinet off him and realizes he wasn't killed by the explosion, he had been shot five times.

He finds some cartridge cases and says that these are an unusual type, there can't be more than a dozen guns of this caliber in this part of the world. Tesland says maybe it'll give them a lead to the murderer, but Bondson says that isn't their problem. All they've got to find is those papers, then their job is finished. He then finds the torch, but sees that the papers are gone. He tells Tesland that the explosion was no accident.

At Tracy Island, Jeff tells Brains he'd better hurry it along with that test, as Alan will be out for his swim soon. Brains says Alan's presence in the water would upset the sonic beam. In the water is a small model submarine, which Brains is controlling. But Alan then jumps into the pool. He tells Brains he's sorry, he didn't realize he was working. Brains says he was just conducting a little experiment.

John then calls in from Thunderbird 5. He says that he's just had an emergency call from a guy named Bondson. Bondson has something to do with the British Secret Service. Jeff says the British Secret Service has its own operators and methods, so why do they need them? John says that Bondson said if they don't help, the entire world could be destroyed. Jeff says that's quite a statement, and wants the details about where they can reach this guy. They'll send one of their agents to contact him.

Penelope is sent to meet Bondson. She travels to Monte Carlo via Fireflash, where she meets Parker, who picks her up in FAB 1. She asks if the yacht is ready, and he says it is. FAB II is anchored off the Spanish coast, and won't be seen until she gives the word. Penelope is pleased, but then says she must make a tele-call.

At his motel room, Bondson receives a sound only call. Penelope says she is an International Rescue agent, and wants him to drive to the Forest of Dean at midnight. He is to come to a clearing 3 kilometers within the perimeter, then he is to wait there. He wants more to go on, how can he know he can trust her? Penelope says he doesn't, but they asked them for help, if he remembers. She suggests they can forget the whole thing, but he says no. It's just he has to be careful in his job. Penelope says so does she.

That night, Bondson drives to the place he was told to go. He's about to leave but then realizes Penelope is behind him. She thinks he's impatient, and tells him to switch off the engine. She also tells him that if he moves a muscle, she'll blow off his head, so he must not turn around. She wants to know why he needs International Rescue. Bondson explains that a fellow British agent collected plans for a nuclear device from a scientist living in a place he can't say due to security reasons. But if these plans fell into the wrong hands, the whole world could be in danger.

Penelope asks if that's what has happened, and Bondson says yes. He was to rendezvous with his colleague aboard his yacht, but it was destroyed before he could get to it, and there was no trace of the plans. The yacht had been sabotaged, and his colleague was murdered before the explosion. Penelope asks how he was killed. Bondson says he was shot five times by a Henretta 45 Supermatic. They must get those plans back. Penelope says it's not International Rescue's policy to involve itself in politics or police work. Bondson says he knows, but they have the most advanced equipment in the world. Those plans must be recovered swiftly, and International Rescue are their only hope. Penelope says she is leaving now, but he is to do nothing or say nothing -she will contact him. She tells him to remain as he is for 10 minutes, then return to his hotel. As she leaves, Bondson attempts to turn around.

A shot from FAB 1 then goes off, as Parker says over a loudspeaker that the lady said don't move. Bondson looks forward again, as FAB 1 then drives away from the forest. Parker asks where they are going, and Penelope tells him to the yacht. She also tells him that was some excellent shooting.

The next morning, Penelope and Parker are on FAB II. Parker brings Penelope some tea. As Penelope thanks him, she says that when they drop anchor, she wants him to go ashore and contact the local newspaper offices. He is to tell them that Gail Williams, the leading fashion model, has arrived on her yacht. She wants him to make certain they print that Ms. Williams is going to expose the murderers and saboteurs who destroyed that vessel yesterday. Parker asks who Gail Williams is, and Penelope reveals she is. Later on, some newspapers carry a story about Gail Williams. Carl reads a story and says this woman is going to track them down... they'll see about that.

He takes his own small boat back to an isolated dock and leaves it there. He puts his diving suit back on and then jumps into the water, where he swims down to get to a submarine waiting at the bottom of the sea.

Inside it are his two accomplices, Ritter and another guy. Ritter says that all this hanging around is getting him down. The other guy tells him to take it easy, as the authorities have got this place bottled up since they blew that yacht. Ritter asks how they'll get past these patrol boats combing the area. Carl then arrives and throws down the newspaper he was reading. He says that some dame is onto them, who has said she's going to try and track them down. Ritter thinks if this woman is just some fashion model then she isn't in their league. But Carl says that report states exactly how many shots were fired, and what type of gun was used. The other guy thinks this is serious, but Carl says so is what they'll do to Gail Williams tonight -she's going to die!

On FAB II, Parker goes to see Penelope. She says she's expecting visitors soon, so he may have the evening off. Parker wonders if that is wise after the news story, but Penelope tells him to go ashore and enjoy himself. Parker thinks a night out could be very profitable, so Penelope says it's settled. As Parker leaves, Penelope takes out her compact and contacts Jeff. She tells him that everything has been arranged. Her bait has been taken, and thinks the plans will be in their hands before midnight.

Jeff asks about her arrangement, and if she's doing anything dangerous. Penelope tells him to stop worrying, but to just be ready for her call. He says they'll be waiting, but tells her to be careful. As the call ends, Penelope sees Parker again. He says he'll be off, but she asks about that case he's carrying. Parker claims he's taking it just in case he wins at the casino.

The case suddenly bursts open, revealing a lot of tools. Parker wonders how they got there. He picks them up and then leaves FAB II via a smaller boat. Penelope says she thinks everything is ready for tonight's guest, she just hopes Parker cleared his stuff out of the way before he left. She then thinks she can hear the sound of another boat approaching.

Outside, Carl arrives at FAB II. Penelope says the fish has taken the bait sooner than she expected, so she returns to her room and waits. She sees Carl in her mirror and tells him to do come in, as it's so nice to have visitors. Carl tells her to get this: this gun is loaded, and he doesn't mind using it. He tells her that she is going for a little boat ride. Penelope says she'll be with him in a moment.

Carl responds by shooting the mirror. Penelope hopes he isn't superstitious, as that's seven years bad luck. He tells her to move and cut the chatter. Penelope says she's ready now, and asks if he'll take her arm. Carl tells her to hold her tongue and just move, fast. They go down the gangway and get back to Carl's boat, which then moves away from FAB II.

Carl takes Penelope back to his boathouse. Penelope thinks this is a deserted area, one just wouldn't know where one was. Carl tells her that soon, it won't matter to her anyway. He stops the boat inside the boathouse and says the pleasure cruise is over. He pulls out a bomb and says this little box of tricks is going to blow her sky high. She asks how it works, and is told that it will be detonated from Carl's sub. So when she dies, they'll be in the clear.

He also says that the delay is all part of the plan. Their sub is stuck at the bottom of the sea, because if they move, the patrol boats will pick them up on their radar. In 90 minutes time, a patrol boat crosses this bay. At the right moment they will detonate the bomb, so the patrol boat comes inshore to investigate the explosion. She will die, whilst they will escape. Carl pulls out some ropes to tie her up with, so she asks if she can fix her face before she dies. Carl tells her to go ahead, since he has time. Penelope pulls out her compact and uses it to send an emergency code to Tracy Island.

Jeff answers the call and sees Penelope using hand signals to reveal she is being held captive at a boathouse, there is a submarine that must be stopped and there is a bomb. Carl then slaps the compact out of her hand, saying she has prettied herself up enough. Penelope asks him to not tie the knots too tightly, as she's very delicate. Jeff and the others wonder what just happened, as all they can see is part of a control panel.

Jeff says the visuals are still functioning, so presumably the sound is still on. He tries turning the sound level up, but they still don't hear anything. Scott suggests contacting her, but Jeff doesn't know what's going on in there. If the wrong person gets the message it could put Penelope in mortal danger for sure. Scott says they should try the code signal, which would be meaningless to someone outside of their organization. Jeff decides to use contact code 5.

A series of tapping noises emit from the compact. Penelope hears them, but so does Carl. He wonders what that noise is, he can hear a tapping noise. Penelope moves her chair to make a noise to try and throw him off. Scott says he just heard something, but then nothing else happens.

Penelope tells Carl that it must have been rats, as these places do have them -he must have some friends. He asks if she's trying to be funny, but she says she was just trying to explain the noise. All of their talk is picked up by the compact, as Jeff and the others hear Penelope ask if those rats will leave the boat before the bomb goes off. Scott says now they know -Penelope os trapped in a boat that's going to get to blow up. Jeff says it's not too late, as they know one of the murderers is still aboard. Gordon says the guy is bound to give himself time to get clear. Jeff sends Scott off and says those killers have got a submarine standing by for something. As Scott leaves, he says they'll need Thunderbird 4.

Jeff tells Virgil and Gordon to get moving, as Penelope is in real trouble. Their machines will have to move faster than they've ever done before. Back at the boat, Carl drags Penelope's chair back away from the compact. He sets the bomb and says this is it. She tells him she was just beginning to enjoy his company, but he says so long -she has about an hour left. He then leaves.

At Tracy Island, Thunderbird 1 takes off, followed by Thunderbird 2. Tin-Tin brings Jeff some coffee. Jeff says he always thinks the waiting is the worst part of the operation. Tin-Tin says she saw Virgil and Gordon fly off. Jeff just wishes he knew more clearly what they are going to find when they get out there.

On the boat, Penelope tries to contact Jeff. Jeff and Tin-Tin realize they can hear something from the monitor, but they can't make out what it is. Penelope is too far away from the compact, and whilst she can hear them, they can't hear her. Jeff asks her if she can get any closer. Penelope starts shuffling on her chair and makes her way towards the compact.

Jeff can't tell what Penelope is up too, he just hopes the compact transmitter can stand up to the treatment. Brains says it should do, the transistors are very small inside the compact, which accounts for the bad reception. But they are extremely robust. Jeff says Penelope is trying to tell them something, he just wishes he knew what it was. Meanwhile, Carl swims back to the submarine and says everything is fixed. All they've got to do now is wait for the patrol boat to cross the bay. In 40 minutes that boathouse, the boat and that dame go sky high!

Scott calls the base and asks if there is any more information. Jeff says he thinks Penelope is trying to contact them, but for some reason she isn't able to get near enough to the transmitter. They then hear Penelope again, but she's still not close enough. Jeff says he still can't make her out, she needs to get closer. Penelope starts moving again. Scott says he'll be at the danger zone in 15 minutes, so Jeff tells him to keep Thunderbird 1 at maximum speed.

Penelope says it's now or never. She starts rocking on the chair left and right, and eventually falls over. She lands right in front of the compact, and tells Jeff that the killers are hiding out in their sub. She doesn't know exactly where they are, but the bomb will be detonated as soon as the local patrol boat comes into the bay at 10 o'clock. The murderers will then slip away with Bondson's plan. Jeff says he'll tell Scott to prepare his sonar equipment.

Scott arrives at the danger zone, so Jeff tells him to proceed with sonar sounding. Scott has the sonar equipment drop out of Thunderbird 1, which is then placed into the water. Scott looks at a monitor for any movement, but there isn't any. He contacts base and says the sonar soundings are operating, but the reading is negative. Jeff tells him to widen the area of search, as he's got to locate that sub.

Virgil says they will arrive 20 minutes from now. Scott asks if he can make it sooner, whilst he resumes his search. Thunderbird 1 starts to move around the waters in a circle, slowly moving the sonar equipment with it. Jeff tells Penelope that Scott is trying to find the sub now, whilst Virgil and Gordon are about 15 minutes away. He says her not to worry, as they'll get her out of there.

Carl says in ten minutes that patrol boat will come across the bay. The other guy asks what'll happen of the patrol boat doesn't investigate once the boathouse explodes. If it doesn't, it'll pick up their sub as soon as they start its motors. Carl says those dumb cops won't be able to resist going, as that bomb is powerful enough to interest anyone. Meanwhile, Scott continues to move the sonar equipment around in the water. He then finally gets a reading.

He tells Virgil and Gordon that the submarine has been located. Virgil says they're approaching the danger zone, and are about to launch Thunderbird 4. Gordon heads down to the pod, as Scott gives the location of the submarine. He also says that they only have five minutes to go. Virgil places pod 4 in the water and leaves in Thunderbird 2. The pod door opens, and Thunderbird 4 heads into the sea.

Gordon says he'll operate the sound scan, and eventually he gets a reading. He tells Scott he knows where the sub is and is heading there at full speed. Scott tells him that sub has got to be paralyzed quickly, before the patrol boat gets to the bay -he has four minutes. Carl says its now three minutes until that patrol boat comes along.

But Gordon has found their sub. He says he's firing the paralyzer now, and a cable shoots out of Thunderbird 4. It attaches itself to the submarine and starts to drill into it. Carl and the others can hear something outside, but don't know what it is. Carl says there's 30 seconds to go, and gets ready to flip the detonator switch.

But they then see something drill through into their sub. It's some sort of pipe, which then starts pumping tranquillizer gas into their sub. Carl says to get the oxygen masks and fire the bomb, but he and the others all collapse before they can. Scott tells his father that Gordon must have knocked those guys out, as the patrol boat is in the bay and nothing has happened.

Scott lands Thunderbird 1 near the boathouse, and unties Penelope. He asks her if she's sure she's alright, as she knew those murderers would try to kill her -she took a chance. Penelope says that's what makes life interesting: the uncertainty. She just hopes Gordon can find the plans alright. Gordon has got inside the sub, and he finds the rolled up papers on a table. He guesses that Penelope can now put Bondson's mind at rest.

Sometime later, Bondson is back at the forest. He hears Penelope's voice, telling him to leave his car and walk to the large tree on the edge of the clearing. He is to keep looking straight ahead, so he sets off towards the tree. He finds the plans, so Penelope tells him to return to his car and be very careful.

Bondson gets back in his car, and says on behalf of his chiefs, he'd like to thank her for her help. She says on behalf of International Rescue, she accepts his thanks. She gives him one last warning: if he makes any attempt to trace her, or her organization, he will find severe opposition. She then gets back into FAB 1, where Parker is waiting. They drive away from the forest and set off for home. She asks Parker how he fared at the casino. Parker says he lost, so she asks how much. Parker says it's a bit difficult.

Penelope says he can tell her. Parker says it wasn't so much "how much" but what it was he lost. Penelope thinks he's being very mysterious, and asks what it was he lost. Parker says he got a bit carried away, but Penelope asks again what he lost. Parker says he lost her yacht, as FAB 1 continues to drive away.