Written and directed by Leo Eaton, it deals with the threat of biological warfare,specifically, with microbial weapons falling into the wrong hands.
A new threat is revealed
At a research clinic in Manchester, England, research assistant Judy Chapman is watching her mentor, a Dr. Denton, conduct a dangerous experiment with a virus called "the K14." Chapman is amazed at how harmless it looks, but Dr. Denton tells her that there is enough of the virus to kill ten million people. He finishes and locks the phial in the safe.
But outside, Captain Black is driving towards the laboratory in a tanker filled with explosive fuel.
After an electronic check at the gates, Judy drives into the road on her way home. Captain Black positions the tanker in Judy's route. She spots it only at the last second.
Despite braking hard, she crashes into the truck and the impact kills her. The Mysteron rings reconstruct her before the tanker explodes.
After a while an exact likeness of Judy Chapman is standing next to Captain Black with handbag and all.
The Mysterons reveal their next threat, which reads, "We have not forgotten your unprovoked attack. To prove how useless it is for you to resist, we will destroy the place of the Angels."
The Spectrum Angels are discussing the Mysteron threat and wonder how the aliens will carry out their threat.
The Mysteronised Judy approaches the gates and after another electronic check drives inside.
She sees the guard and uses the arms that are for holding test tubes in safety to choke the guard to death. Afterwards she goes inside the lab and steals the phial of K14 virus.
Colonel White sends Captain Scarlet and Captain Blue in a Spectrum Passenger Jet to investigate the strange goings on at the research clinic in Manchester. Captain Blue notes that the Rhapsody Angel once lived there, but Captain Scarlet hardly sees it as the place of the Angels.
They find Dr. Denton, who tells them he is sure that Judy has stolen the virus because she was the one person to enter the building on that particular morning.
He tells them that the K14 is the deadliest virus developed and if the phial is broken, it is most likely to kill ten million people.
Judy is on a plane with the K14 stored in her handbag. The Captain says that they will be landing at New York Airport in ten minutes.
The two Spectrum agents return to Cloudbase. Captain Scarlet reports to Colonel White stating that the doctor will also come in an hour. Colonel White asks if there is a cure for the virus. Captain Scarlet replies that the doctor says that one will be found, but it would take months to develop. The virus is so deadly that the human body has no defence against it.
Lieutenant Green suddenly reports that the Mysteronised Judy has landed in New York. Colonel White sends Captain Scarlet and Captain Blue there straightaway, and tells Lieutenant Green to launch all the Angels.
The Spectrum Headquarters in New York reports to Captain Scarlet telling him that Judy has driven to inner state highway in a Saloon car registered 104X238. The agents land and requisition Spectrum Pursuit Vehicle 021 to drive after her.
Symphony Angel reports that Judy is still driving on the interstate highway, and the SPV drives in that direction. But Captain Black is watching. He warns Judy that Spectrum's vehicle is less than five miles behind her, and tells her that she knows what she has to do.
At Cloudbase, Colonel White is reassuring Dr. Denton that the phial will be retrieved safely. The doctor replies that millions of lives depend on his judgement.
Judy stops the car and climbs out, then allows the car to go off the road and crash into a tree. Captain Scarlet and Captain Blue see the car crash and go down to investigate with their guns drawn. They see no sign of their suspect, but they do find what looks like a shattered phial of the virus.
Back at Cloudbase, Captain Scarlet and Captain Blue are in the sick bay. Colonel White says that even though Captain Scarlet is, presumably, immune to the virus, everything must be done for Captain Blue. Dr. Denton is sent to the scene of the crash performing a spraying operation to see if the virus was released. All of his results come back as negative and he returns to Cloudbase.
Colonel White now understands that they have all been tricked, and that Judy still has the virus. He tells Lietenant Green to issue a Red Alert while he goes down to the sick bay to inform his men. (When he does this, it marks one of only two times Colonel White is actually shown wearing his radio-cap; the other is during "Flight to Atlantica," aboard the Spectrum Passenger Jet he and Captain Scarlet are flying.)
Later Captain Scarlet looks at his watch and admits that there is still no trace or clue to the Mysteron threat. Suddenly Lieutenant Green says that Judy has been sighted in Goosebay, Canada.
After the Colonel goes over how many places she has been, Captain Scarlet finally figures it out when the Colonel says "Los Angeles" and says that "Los Angeles" means "The Angels." (Since Gerry Anderson's backstory ascribes linguistic skills to Captain Magenta rather than Captain Scarlet, how the latter figures this out is not explained.)
Captain Scarlet departs straightaway for Los Angeles with Captain Blue accompanying him. Colonel White later reports that Judy has been seen driving away from the city to the main reservoir at the Boulder/Hoover Dam, where she will pour the virus into the city's water supply--the quickest way, and among the deadliest, to spread the virus.
Judy drives to the Boulder Dam, rummaging in her hand bag to reveal the phial with the virus.
With little time to spare, Captain Scarlet parachutes out of the SPJ to land on the dam below from 500 feet. Unfortunately, Judy sees the SPJ and shoots Captain Scarlet before he lands, which weakens him.
Judy fumbles in her handbag and gets out the phial, which she intends to drop into the reservoir. Captain Scarlet aims his pistol at her, shouting for her to stop. The Mysteron agent says that he is too late.
Captain Scarlet warns her that if she makes one move he will shoot. Judy takes a step backward, and Captain Scarlet fires a shot, making good on his threat. As she is walking back, one of her high heels gets caught and breaks off on a drain, causing her to lose her balance and fall off the dam to her death.
The phial is just on the edge of the dam and after careful reaching, Captain Scarlet barely retrieves it in the nick of time, without any of its contents spilling into the water. Colonel White calls in, anxious to hear from him. Captain Scarlet assures him that everything is fine and says "The city of the Angels is safe."
- In 1993, the instalment was also a small paperback in a series of eight books, written by Graham Brown, illustrated by famous artist Richard Chasemore and published by Boxtree, with the title: Place of the Angels.