"Point 783" is the fifth produced instalment, and the thirteenth transmitted instalment, of Captain Scarlet and the Mysterons. In it, the Mysterons attempt to assassinate the Supreme Commander of the Earth Forces, using a prototype of a new tank as their weapon.
Target: The Supreme Commander
In an army station in the Sahara Desert, two Earth Forces personnel, General Cope and Captain Hassel, are conducting tests of their latest weapon, "The Unitron," a new, almost-indestructible tank. The two look on with satisfaction as the Unitron blasts a decoy target of army machines and drives straight through the burning wreckage without so much as a mark. Hassel asks Cope if the Supreme Commander will be satisfied with the results. Cope assures him that he will be delighted.
Meanwhile, the Mysterons are sending their latest threat. "We have not forgotten," it reads. "We will assassinate the Supreme Commander of Earth Forces within the next twenty-four hours. Supreme Commander, you have only twenty-four more hours to live."
Later at Cloudbase, Colonel White talks with the Supreme Commander, who asks him if anyone is safe from these "Mysterons." The Colonel assures him that they will do their best to protect him. Unsure of all this, the Supreme Commander goes on to tell him that he is expected at S.H.E.F., the Supreme Headquarters of the Earth Forces, in New York. Colonel White orders Captain Scarlet and Captain Blue to escort the Supreme Commander there safely, along with the Spectrum Angels. After Lieutenant Green launches all the Angels, they are all well on their way with the two Spectrum agents taking the Supreme Commander in a Spectrum Passenger Jet.
In another area somewhere else, two of the Supreme Commander's men, Major Brooks and Colonel Storm, are driving to New York. Storm complains that they are behind schedule, but Brooks replies that they had had a late start. Storm goes on to say that it is still no excuse for tardiness, noting that the Supreme Commander demands punctuality and so does he. Speaking into his radio communicator, Brooks reports back to base saying that they are approaching Catskill Tunnel and that their Estimated Time of Arrival at New York will be at 06:00 hours, 6:00 AM civilian.
Coming from the opposite direction, two workmen in a petrol, or gasoline, tanker are on their way towards the mountains. One of them turns to his co-worker, whom he calls Pete, and tells him he will be extremely glad to be up there because of the heat in their previous location.
The two S.H.E.F men arrive at Catskill Tunnel; there, the light is green, showing that they can go. They drive into the tunnel. Meanwhile the tanker reaches the tunnel as well, with the first worker gazing at the red light and complaining that they will have to stop and wait. But Pete, who is driving, goes on straight through--much to the astonishment of his friend, who sees that he has a look of a person in a trance, and orders Pete to stop before they hit something. The S.H.E.F car is still in the tunnel, with the tanker driving towards them. Suddenly the lights of the truck dazzle the two men, who attempt, vainly, to shield their eyes. The two vehicles crash into each other and a massive explosion kills all four, filling the whole tunnel with flames. Twin green rings then sweep the corpses of Brooks and Storm, and soon exact likenesses of the men leave the tunnel with their car driving in the direction of New York.
The First Attempt
At S.H.E.F, the Mysterons' likeness of Major Brooks is in the original's office, waiting. When the Supreme Commander, Captain Scarlet, and Captain Blue arrive, the Brooks likeness apologizes to his Supreme Commander for not meeting him at the airport and is introduced to the two Spectrum agents. The Brooks likeness goes on to say that they should go through processing because their conference is waiting for them. He leads them on an escalator and through a sliding door. Suddenly Captain Blue notices that Captain Scarlet is acting strangely, as though he is feeling unwell. They finally reach the processing area, where all four men give their identifications to a computer. After these identifications have been read and cleared, with the Brooks likeness hurrying them all along, they finally reach the top of the building.
The conference begins with the Supreme Commander explaining about their latest weapon, "the Unitron," with Captain Scarlet still acting strangely. Suddenly the Brooks likeness reveals himself to be a Mysteron, and Captain Scarlet quickly presses an emergency button on the table at which they are sitting. While the Brooks likeness becomes a living bomb with smoke pouring from his coat, protective glass panels lower on top of all the men shielding them. The Brooks likeness explodes and great chunks of rubble fall from the ceiling covering the whole room.
The Arrival at Point 783
Later, Captain Blue and the Supreme Commander are driving to Point 783 in the Sahara Desert. The Supreme Commander is amazed by all that has happened and asks Captain Blue, "Do you mean to tell me that it was Major Brooks himself who exploded?"
Captain Blue nods and explains that the Mysterons can use their powers of retro-metabolism to re-create an exact likeness of any object or person and use them for their own objectives, so they had used a likeness of Major Brooks to kill him. Had Captain Scarlet not pressed the emergency button, they would all have been killed in the explosion. The Supreme Commander asks how Captain Scarlet knew, and Captain Blue continues to explain that his friend has a strange sixth sense about the Mysterons. Still confused, the Supreme Commander tells him that he will be more relieved when they reach the Command Base. However, Captain Black is watching them, and he relays instructions to the Colonel Storm likeness, who is at the Command Base at that very moment with General Cope and General Hassell, telling him that he knows what he must do.
After they finally arriving at Point 783 and giving the field word, Captain Blue and the Supreme Commander go into the base. There, the Colonel Storm likeness, greeting them, aims a gun at them. Captain Blue is about to draw his own gun, but the Colonel Storm likeness assures him that it is not loaded and goes on to say that it is a new weapon called a rapid automatic; he says that the Supreme Commander would like to look at it. The Supreme Commander interrupts him and orders him to begin the demonstration of the Unitron.
The Unitron Project
The Supreme Commander asks Captain Hassel and General Cope to start the demonstration. They watch the tank destroying a decoy target of army machinery and go straight through the flames. Cope tells the Controller that the Unitron is used for computer-controlled mechanized forces, not live personnel. The Supreme Commander continues to look at the screen and seems most impressed. Cope goes on to explain that it can operate on any terrain, overcome all obstacles, and operate unmanned. After the Supreme Commander asks how it is controlled. Cope replies that it can either controlled by a trained operator or programmed to seek and destroy a chosen target automatically.
Captain Blue suddenly gets a transmission from Colonel White who asks if there is anything to report. Captain Blue tells him that Phase 1 of the operation is going well. Colonel White says that the Angels are patrolling the area and Captain Scarlet is standing by for further orders. The Commander wants to take a closer look at the Unitron and asks if they can see it on the Observation Point. Captain Blue objects to this saying that they are taking an unnecessary risk. The Colonel Storm likeness assures him that nothing will happen to the Supreme Commander while he is under the protection of Spectrum and bids Captain Blue not be so jumpy. He leads them all to the Observation Point.
They all watch while Captain Blue observes through his binoculars. The Supreme Commander sees the tank heading straight towards them, and it suddenly opens fire on the base. Captain Blue motions them all inside, telling him that this is no demonstration. They all get inside just in time. Captain Blue contacts Colonel White on the situation. Colonel White orders Lieutenant Green to bid the Angels destroy the Unitron as a hostile target. The Supreme Commander immediately asks Captain Hassel why the Unitron is attacking. Hassel responds that it is out of his control and that someone has so programmed the computer control as not to allow it to stop till it has destroyed its target, which seems to be their base.
Meanwhile, the Angels proceed to attack the Unitron, but it survives several impacts from the missiles of their aircraft and simply keeps on going. With only ten minutes left before the base is completely destroyed and the Unitron now using its flamethrower, the Supreme Commander says that it is now all up to Spectrum.
In another area of the Sahara Desert, Captain Scarlet enters a shop, whose keeper he sees talking on a telephone. He goes over to him and, after presenting his identification, is pointed in the direction of Spectrum Pursuit Vehicle 428.
The Unitron continues its attack, and Captain Blue tells Colonel White that the base cannot survive much longer. Colonel White says that Captain Scarlet will be with them in six minutes and that they must do exactly as he says.
After he drives the SPV out of the shop, Captain Scarlet goes in the direction of the base and reports to Colonel White that he is on his way. Colonel White explains the situation and tells Captain Scarlet that his assignment is to get the Supreme Commander out and away at all costs. The Angels are still firing at the Unitron, but it still remains undamaged. Captain Scarlet arrives and orders Captain Blue to bring out the Supreme Commander straight away. Captain Blue agrees and tells the Supreme Commander that there is an SPV outside and he must leave right away. He gives the Colonel Storm likeness the responsibility of looking after him and the latter, convinced that this Earthman has practically delivered the Supreme Commander directly into Mysteron hands to be assassinated, willingly accepts.
On screen they watch the SPV drive away. But suddenly the Unitron hits one of the walls of the base, panicking Captain Hassel. To everyone's amazement, the Unitron changes its course, going in the direction of the SPV. Hassel tells them that it means that whatever it is homing onto is aboard the SPV. The SPV drives through the desert, with the Unitron still attacking it. Captain Scarlet cannot understand why it altered course and came after them. Suddenly the Colonel Storm likeness draws his gun, revealing himself to be a Mysteron agent and mocking Captain Scarlet, "Where's your sixth sense, Earthman?" Captain Scarlet suddenly realizes that the Colonel Storm likeness is to blame for all this. The Colonel Storm likeness aims his gun at Captain Scarlet, telling him not to try anything.
Despite this, Captain Scarlet proceeds to draw his own gun, but the Colonel Storm likeness shoots him three times in the chest. Extremely weakened and dying, Captain Scarlet pulls the emergency switch that activates the ejector seats where he and the Supreme Commander were sitting, blasting them safely out of the SPV and leaving the Colonel Storm likeness behind with the Unitron still chasing him. The parachute-equipped ejector seats land safely on the ground while the SPV and the Unitron both drive off a huge cliff, which destroys the Mysterons' likeness of Colonel Storm and causes the tank to explode. The Supreme Commander dabs at Captain Scarlet's wounds and sees that he is losing a lot of blood. He promises to take him to a hospital as soon as possible.
But instead, later at the Command Base, a Spectrum Helicopter arrives and takes Captain Scarlet away, with the men discussing the situation. General Cope is amazed that Colonel Storm had programmed the Unitron attack on himself, and asks Captain Blue if the Mysterons will continue attempting to kill the Supreme Commander. Captain Blue assures them that the Supreme Commander is safe, now that the Mysterons have failed, and they will chose another target. The Supreme Commander suddenly enters the room and dresses down Captain Blue; he is furious that, as far as he can perceive, Spectrum acted disgracefully in waiting three hours for its helicopter to help Captain Scarlet, and probably guaranteed his death. General Cope agrees, saying that Spectrum needs every man it has against the Mysterons. But Captain Blue, knowing that Captain Scarlet's retro-metabolic powers will enable him to recover, assures them that he will live and continue the fight against the Mysterons, maybe sooner than either of them thinks.
The interior of the Command Base is believed to have been the model for the interiors of S.H.A.D.O. in UFO, Gerry Anderon's very first live-action television programme.