After a robbery in his london shop, antique dealer John Mannering a.k.a. The Baron, is persuaded by Templeton-Green to work for Diplomatic Intelligence. He travels behind the Iron Curtin and meets his contact Cordelia. They encounter a corrupt Party member who attempts to frame them for the murder of his lover, the London jewel thief.
Mannering attends the funeral of Jim Carey, a former army colleague. After receiving a message that Carey is still alive, Mannering agrees to go undercover for Templeton-Green. An elaborate plan to steal a $ 1 m jewel is bad enough but becomes worse when Cordelia is used as a hostage to ensure that the Baron cooperates with Carey.
The Baron does a deal with a scheming insurance agent to recover a £ 100,000 Aztec mask from an ex-con. However the former crook's gang leader has a different idea and will even hurt his one-time friend's daughter to get the mask.
When Mannering gets a message to buy The Four Horsemen, he travels to Khakania, a country gripped in civil war. The Horseman are a famous statue worth over $1m. The money from the statue will help fund the rebel cause. The Baron tries to flee the country with the rebel leader's daughter and statue but is hounded by the secret police who are always one step ahead of him.
An undercover British agent is caught in an Eastern Bloc country and names Mannering as his contact. The Baron and Cordelia are in the country to pass over some money. They are warner not to go to the rendezvous by Bradfield as it is a trap. Cordelia is caught and held by the police. Mannering has a plan to kidnap the head of the police but there is a double agent in the Bradfield house.
Mannering is invited by Sir Frederick Alton to his country home. When he enters the house he hears a woman crying for help. As he goes to help he's knocked unconscious. He wakes up to discover that he has a twin double. Mannering manages to change places with the double and his captors kill the man they belive to be the Baron. They then let him in on their plans to steal the Crown Jewels only for Cordelia to turn up at the wrong moment.
The Baron has to convince Cordelia who he is, but he still has to play the part for his captors. He manages to get rid of Revell and the gang head to London. However, one of the gang is the best friend of the part Mannering is playing. After he's discovered, the Baron really has to steal the Crown Jewels.
David Marlowe is kidnapped from Mannering's shop. For his release he must sell a false Renoir to Sir Robert Ellacott. Mannering calls on Templeton-Green for help. The Baron follows his orders and sells the picture but whilst visiting he meets Sir Robert's nephew Roddy and becomes suspicious. When Marlowe is stabbed by Roddy as he attempts to escape, the other gang members become nervous. Mannering has to meet Roddy with the ransom money to ensure that Marlowe isn't killed.
The Baron and Cordelia are in Switzerland when they bump into Peter Franklin, an old friend of Cordelia. Franklin, who is a CIA agent, has stolen the latest strain in a deadly virus from the laboratory he was working in. When Franklin is killed, Mannering is in a race with Sorenson, the scientist who developed the virus, and Holmes, an unscrupulous character, to discover the whereabouts of the deadly bacteria.
Mannering is asked by an eccentric millionaire to witness him purchase The Legions of Ammrak, a golden necklace that contains seven perfectly matched black pearls. The Baron identifies that they are genuine but David Marlowe notices that the seller, King Ibrahim, is wearing the wrong school tie. When Mannering realises that he's being duped, he has to recover both the money and the necklace.
The sale of a 5000 year old Samurai sword gives the Baron trouble. When the seller, Asano, bumps into an old enemy, Norman Sterling, at Mannering's apartment, Sterling promises to avenge the treatment of him and his brother in a Japanese POW camp. After Asano is murdered, the Baron has to protect Sterling from Asano's loyal servant is out for revenge.
Mannering stops up to pick up a petrified girl in a country lane, as they drive away they are shot at and crash off the road. When he comes to, he keeps having flashbacks that feature weird objects but the police simply think that he is suffering from concussion. As he tries to retrace his footsteps, he is watched by a man with a gun who is determined not to let him near the house in which the girl is held hostage.
Louisa Trenton, an old friend of Mannering is in trouble. When she sells the Baron some rare family miniatures he offers his help but she declines. Later when she calls for his help he rushes to meet her in a London club only to find that she has been murdered. When he investigates he discovers that she was being blackmailed by her young lover. He is only the fall guy but as Mannering tries to find out who is the boss, more people are murdered.
Mannering gets a tip-off that there will be a robbery at the Lynstead Collection. The police and the Baron lie in wait but one of the policemen is killed by the gang leader, Greg Wilde. Wilde is arrested for murder but his crooked solicitor tells him that all of the witnesses will be disposed of. Mannering escapes an attempt on his life but Wilde escapes from police custody and is out to get the Baron.
The Baron and Cordelia are at the Macao docks checking a shipment of antiques. A missing crate leads to Cordelia witnessing a murder on baord a cargo ship. When she is held prisoner Mannering has to stow away on the ship. They meet an undercover CIA agent working as one of the crew who tells them about the ship's mysterious cargo and its secret destination. The CIA agent is killed and Mannering forced out into the open.
With the ship arriving at the island to deliver its cargo, Mannering learns of the plot to steal an American space capsule. Via the ship's radio he alerts the US Navy of the plot. He and Cordelia escape and they must think up a plan to stop the robbery and hope that the Navy can get to them in time to assist.
The Vitale family are in possession of an emerald cameo brooch,which is said to be cursed and brings death to its wearer. Cristina Vitale arranges to sell it to Cordelia but she is killed before the transaction can be completed. Soon afterwards,her father is also slain. As the new owner of the brooch Cordelia is now in danger but is the curse genuine or a cover for something equally as sinister?
Nikki Holz sets out from Germany to London with important information for Mannering but she is abducted before she can meet up with him. Mannering and Cordelia learn that her captors are members of a neo-Nazi organization who are selling off art treasures in order to fund their attempts to gain dominance in Europe, a discovery which leads the Baron into a dangerous climbing adventure.
The Petrograd icons have been stolen but Mannering tracks them down and is about to put them into a safe deposit box when he is knocked unconscious and,on coming to,finds that they have been stolen again. His investigations lead him to the urbane Jim Gaynor and the Peerage gentlemen's club,where Mannering engages in a game of poker - the stakes being the further recovery of the icons.
Delivering a consignment of Medicis to a wealthy female client,Mannering discovers the door open,the lady missing and a strange man inside. Investigations reveal that she had been giving money to a bizarre religious sect with which she had recently been involved,whose leader styles himself the Chosen One. When Mannering decides to look into the sect he finds that he has become the one they have chosen to be killed.
Mannering is approached by a glamorous French widow,Madame Devereaux,who sells him an expensive necklace,the seven eyes of night. after she has gone,however,he realizes that she is an impostor and a member of a gang duping buyers into believing they have bought something valuable. He hopes to get to the gang by following secretary Nancy Cummings.
Mannering has sold some antiques on behalf of Madame Nicharos, the wife of a deposed Balkan president. Before he can deliver the money to her he is confronted by the general who led the coup. The general seeks both the money and Madame Nicharos in order to strengthen his hold on power.
It would appear that the Mona Lisa has been stolen from the Louvre. But is it the actual Da Vinci painting or a forgery substituted to thwart the thieves? One of the robbers flies into London secretly and arranges to meet with Mannering so that he can authenticate the spoils whilst a French spy bugs the Baron's phone so that he too can find out further details. Ultimately Mannering finds himself the prospective saviour of one of the world's most iconic paintings.
Cordelia travels to South America on Mannering's behalf to meet an explorer who has something to tell them. Then she disappears and Mannering travels out to find her. He discovers that she has been arrested for discovering a secret that the authorities do not want to come out into the open,involving the stock-piling of hidden weapons.
Mannering is about to give a valuation for a client when the man dies. He is a former bullion robber and he has been murdered by Ashton,his erstwhile partner in crime who is looking for the hidden loot and intends to use the dead man's daughter in order to locate it. This leads the Baron and Cordelia to an old dark house in the country where mysterious goings on have been reported.
At a party in his house gangster Mario Navini kills Pia Vallachio and,helped by his younger brother Bruno,disposes of her body in a quarry. They are observed by sole witness Maria Pullerno,who flees in terror. The Italian Minister of Justice,Vittorio Guardi, asks Mannering to obtain a witness statement from her,as a result of which the Baron and Maria end up besieged by the Navinis in the police station in the village of Santa Montena.
When Mannering learns that the manager of his Paris shop is shipping illegal narcotics in the base of antiques he ships abroad, he joins forces with the police to break up the drug trafficking ring.
In Scotland Douglas MacRae,another antique dealer and friend of the Baron,is murdered by American mobsters who intercept him in the course of a 'job he has to finish'. Though the coroner's verdict is one of accidental death,Mannering is not convinced,especially when he spots one of the gangsters wearing Douglas's ring. His pursuit of the gang exposes a plan to flood the country with counterfeit money.
The Baron is to meet Stanley White, a man he has never seen before,for information about a valuable sword. However film-maker Arkin Morley is also after the sword and has Mannering abducted and imprisoned in a railway goods truck whilst Compton,one of his men, posing as Mannering, makes the contact with White. Mannering has to escape and intercept Compton before he gets to White.
An airline steward is found dead with a gold medallion in his possession - it is one of several stolen from the Vatican and links him to one of the biggest art smuggling rings in the world. To investigate it the Baron travels to Rome,meeting up with ex-girlfriend Cathy Dorne,who is being forced by her boss Nick to be part of the smuggling gang and who helps Mannering bring its members to justice.
