Louisa Trenton is an old friend of Mannering and she is clearly in financial trouble because she offers to sell him some miniatures which are very valuable and have long been in her family. Later she rings the Baron,who goes to meet her at a discotheque,but finds that she is dead. The police believe that she killed herself but Mannering is certain that she was being blackmailed - and that the blackmailer murdered her. He has several suspects to choose from.
Having received a tip-off that the Lynstead art collection is about to be burgled Mannering lies in wait with the police for the thieves but one of the officers is shot and killed by gang leader Greg Wilde,who subsequently is charged with murder and sent for trial. As the only surviving witness to the killing, Mannering is in a vulnerable position when Wilde escapes from custody and comes after him with murderous intent.
Mannering and Cordelia are in an Iron Curtain country where they are about to hand over some money at a secret rendezvous. However Mannering's contact has been caught by the police and forced to name his contact. Though warned to keep away Mannering and Cordelia fall into a trap and she is taken by the police. Mannering plans to spring her by taking his own prisoner - the chief of police.
When the beautiful woman who stole a priceless Faberge bauble from his shop is identified as a Pameranian courier, Mannering decides to visit the country's embassy and demand satisfaction. He is intercepted by British intelligence agents who convince him to go behind the Iron Curtain and break up the ring of art thieves who have been hiding behind diplomatic immunity, using his real occupation as an antiques dealer as his cover.
Asano, an aging Japanese man, agrees to sell a family heirloom, a 500-year-old samurai sword, to Mannering for 10,000 pounds. When Asano delivers the sword to the antiques dealer, he bumps into Sterling, an British army officer who suffered the Japanese POW camp commanded by Asano. Sterling plans on exacting revenge for his treatment at the hands of the Japanese soldier and when Asano is found dead, Mannering must project Sterling from Asano's vengeful servant.
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.
Having attended the funeral of his old Army buddy,Jim Carey,Mannering is surprised to learn that the man is far from dead and the funeral was but a smoke screen. Carey is planning to steal a priceless jewel from a museum and wants the cooperation of Mannering,initially as a fence,later as a gang member and,to ensure his cooperation, Carey takes Cordelia hostage.
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.
Whilst in Switzerland Mannering and Cordelia meet Peter Franklin, an American undercover agent and an old flame of Cordelia. He has stolen a strain of a deadly germ warfare virus from the laboratory where he was secretly working. When he is killed and the virus goes missing, Mannering intends to get to it before Dr. Ingar Sorensen, who developed it and the unscrupulous free agent Holmes.
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.