On an island near Greece, UNCLE Agent, Mark Slate watches as a Thrush agent tests a new drug by spraying it on some partying villagers. The drug slows them to half speed. If the drug is unleashed on the world, ecomonic chaos would ensue. The only known antidote is on its way to the Island via commercial flight ... on the fleas of a dachsund accompanied by UNCLE Agent, April Dancer.

Zalamar is a tiny but very important Arabian State. Mark is there to protect it's ruler, Ali Hassen, after rumors of trouble. Unfortunately, Mark is unsuccessful. Ali Hassen succumbs to poisoned popcorn and his daughter, Fatima, who is next in line to rule, is kidnapped. April, a dead ringer for Fatima, is sent to Zalamar to impersonate Fatima until she can be found and released from her captors.

UNCLE Agent Napoleon Solo is in London with April where they are to pick up instructions in the form of a half-penny in a beggar's cap. Unfortunately, Solo was followed from the airport by Mother Muffin, an elderly lady who leads a group of assassins bent on retrieving the half-penny first.

Someone is after belly dancer Mata Hurens, who has a message for Mr. Waverly. She boards a train for London as does April who is trying to see to her safe arrival. However, a bomb has been planted on the tracks. The train derails and many are killed, including Mata Hurens. April survives and is determined to find the murderer. By impersonating the dead bellydancer, April hopes the killer, thinking he's failed will make another attempt. Then, April and Mark can capture him.

UNCLE headquarters in Rome is raided by Thrush agents who swipe a small, jewel-like device called a Montori. The Montori allows UNCLE agents to listen in on any UNCLE channels, even scrambled ones. Waverly orders all communications at UNCLE to cease until the device is recovered. With six world leaders coming together for a top-secret conference, Waverly believes Thrush intends to create chaos at the meeting. Without communications, Waverly is unable to warn the world leaders of the probable danger. April and Mark must find the device.

Mexican millionaire and bullfight aficionado, DeSada, is head of Thrush:Central America. In an effort to gain control of Project Gamma, a rocket transport capable of 5,000 mph, he has kidnapped the three men who have created it. Meanwhile, his own scientist has develped a machine capable draining a brain of all its knowledge and transfering to a computer tape. April has made contact through one of DeSada's helpers, a famous matador. Mark takes on the persona of a bullfight critic to aid April in freeing the three kidnap victims.

Mark and April are sent to Denmark to rescue Stanley Umlaut who has been kidnapped by Thrush. Stanley, unknowingly, has eaten a piece of Danish blue cheese that contains a microdot hidden by Thrush agents.

A doctor developes a serum that is able to transfer the mind of a dead person into the brain of one of his descendants. The doctor is murdered by members of a cult who kill by scratching their victims. The Cambodyses cult are fed small amounts of poison on a daily basis until they are immune to its affects. However, it renders their finger nails deadly weapons. The cult, Thrush, and UNCLE want the serum and the doctor's granddaughter.

April and Mark are looking for Professor Antrum who has been searching for Atlantis. Rumors indicate that crystals able to concentrate the power of the sun into a beam more powerful than a laser are hidden at the entrance to Atlantis. According to a cryptogram that entrance is on the property of an eccentric name LeGallows. Antrum is kidnapped by Thrush and recovered by UNCLE only to be re-kidnapped along with April and Mark.

Thrush is determined to crush the economies of the countries bordering the Pacific by creating new submarine smuggling lanes. They finish laying out the plans on a ship in the South Pacific. Mark swipes the plans and instigates a mutiny. April and Mark are forced to abandon ship and the plans are lost. April washes up on a tiny Island and is captured by the ruler. Mark to the rescue! Unfortunately, the ship's captain also survives the wreck and washes up on the island.

April is tied atop a car being attacked by an eagle as part of an experiment by a retired Thrush agent, Gita Vlander. From inside Gita, Thrush agent Egon, and Gita's scientist watch. The scientist has a molecular reorganizer and aims it at the eagle. The eagle vanishes and turns up in a cage behind Egon. Gita assures him it works on people, too.

The owner of Circus Sadvaricci returns to his circus after a financial killing and is confronted by the Countess who knows he has caused her financial ruin. Sadvaricci kills and buries her when she threatens to expose him for stock market manipulation, enter UNCLE. April goes under cover in his circus as an aerialist.

A big time gambler, Joey Celeste, has contacted UNCLE with an offer to inform on his bosses. April is sent to Italy to escort him to UNCLE headquarters. However, his old bosses have learned of his intention. They hire a notorius hitman who has never failed to miss his mark to eliminate Celeste.

Professor Quantum has created a seemingly useless machine that extracts the color out of everything in it's wake. A stranger, however, offers the Professor anything he wants in exchange for the Light Variator. April, posing as a lab assistant, has been sent to keep an eye on Quantum and he has fallen in love with her. The professor decides that what he really wants is his ""lab assistant"" and he's willing to turn over the machine if his wish is granted.

A crime syndicate learns that it is being investigated by April. The boss, Dossetti, orders her killed but one of his men finds her appealing and kidnaps her to be part of his harem. The syndicate intends to create a diversion with a UFO and to raid the Royal Palace.

UNCLE has received information on an attack by Dr. Vladimir Toulouse. He has created a pill that gives superhuman strength to anyone who takes it and has threatened to unleash a superhuman army unless a ransome is paid.

April and Mark are in Venice to capture Horsch, a top-ranking crook. April manages to grab him and the three set off for the Yugoslavian border. When border guards board the train on which they are passengers, Horsch escapes. April gives chase, following him to a villa where she is captured and drugged. Meantime, Mark is trying to trace April and they eventually uncover a plot to loot the Vatican.

The King of Drublegratz is dying. The heirs to the throne are his three sons, but THRUSH wants to take over the country. They send Dr. Igor Gork with his sound projector. As one of the sons drives across a bridge, Dr. Gork uses the projector to destroy it. April and Mark are sent to prevent any further deaths in the Royal Family.

Mark and April arrange to meet an informant who claims a politically important woman is in danger at Rejuvena Isle. However, two killers with an odd gun shoot her first. When Mark and April arrive, the informant is dead, having expired from old age though a very young woman. It is discovered that Baroness Blangstead offers the fountain of youth, her wonder drug, to those who can pay her price: Official Secrets.

Thrush Agent Mother Magda is plotting the elimination of world leaders and planning to replace them with exact doubles. Mark loses the tape with all the details as to how it will be done. April and Mark must recover it immediately.

The Utter Anguish Gold Mine is up for grabs when the owner dies. The mine contains a huge vein of Triterian crystals that can be used to make death beams from laser light. Thrush and UNCLE are VERY interested in acquiring the mine.

A retired gangster from Chicago is second in line to rule a small Mediterranean country. He assassinates the Duke leaving only one person in his way, Major Stella who is currently saving souls in London. Mark and April are sent to persuade her to save her country.

A French School for Civil Administrators always plans a commando exercise for its graduating students. Waverly knows that there is some kind of hijack being planned so he sends April and Mark to investigate.

A former classmate of Waverly's owns a bodyguard service. When one of the clients is murder, only the body guards are present but they don't recall it happening. Waverly sends April and Mark investigate.

Thrush has developed a new mobile force that enable them to disrupt UNCLE operations. Mark infiltrates the group and tapes their transmissions. He makes his getaway, hides the tape in his rented car, and contacts April but he is shot in the leg. The car and tape are stolen by a man who overhears his transmission to April. Mark is taken off the case; April is assigned the case.

Waverly believes that a Japanese war criminal is active again. Mark and April go to Hawaii to investigate their only lead, his sister. When their informant is killed, it's obvious to Mark and to April that the sister is involved.

April poses as an airline stewardess; Mark is disguised as a big game hunter. Both are on board a plane carrying a number of scientists to a Council of World Scientists meeting. One doctor aboard has developed a substance that, carried by harmless birds, can cause slow death to humans. Also on the same flight is the doctor who has developed the antidote. Waverly fears a confrontation between the two hence April and Mark on the scene.

Mark inherits a home in England. April, who is key witness against a Thrush Agent, has been threatened. Waverly suggests April stay with Mark until the trial. Unfortunately, a plot is afoot to kill Mark so that the stately home can be inherited by another relative.