The Protectors are three independently wealthy private detectives - American Harry Rule, living in London, Caroline who was married to an Italian Count and Paris-based art expert Paul Buchet. They are approached by Freddie Reiwald, a scientist working on a means of perfecting synthetic gold, whose four colleagues have all died in mysterious circumstances. Freddie is about to perform a stunt parachute jump with a man called Ransome, and the killers have abducted Ransome's girl-friend, threatening to murder her unless he lets Freddie die. The Protectors must find her ...
The Protectors are hired by millionaire business man Bela Karolian to spring his younger brother Sandor, who was imprisoned on trumped-up charges. Although the prison break is successfully accomplished it becomes apparent that Bela only wants Sandor back for one reason - to kill him and thereby stop him from exposing his elder brother as a large scale drug dealer.
A senator investigating organized crime in Rome, with a view to catching gang boss 'Il Gufo' or The Owl, is abducted and on release planted with photos which will incriminate him. The only witness to the abduction is an elderly blind man. Caroline goes in search of him but finds herself face to face with Il Gufo himself.
Brad Huron has made a bet with his friend - that he will be able to vanish off the face of the earth and nobody will be able to detect his whereabouts. He asks the Protectors to help him accomplish this but Harry refuses. Caroline, however, is keen to prove a point and goes on the run with Brad. Then Brad's father tells Harry that his son is a dangerous paranoiac with murderous tendencies and Caroline is in danger.
President Medina has come for urgent medical treatment in the Mediterranean and his wife fears that his political enemies will use the opportunity to abduct him. Harry arranges for decoys to impersonate the president and his wife whilst Medina is smuggled ashore secretly but clearly somebody has got wind of the plan as the ambulance carrying Medina to hospital is hi-jacked.
In investigating the brains behind a plot to overthrow an island government, the Protectors are joined by Jim Palmer, an old flame of Caroline. He suspects the chief plotter is night club owner Adam Markos on whose premises guns are found but Harry believes that Jim is leading Caroline in the wrong direction and has his own suspicions as to the true culprit behind the plan.
The West German government ask the Protectors' help to trace the mysterious benefactor providing pensions for five former Nazis. Prime suspect is wealthy Hans Keller and Caroline intercepts a letter from him, bearing only the words The Quick Brown Fox Jumped Over the Lazy Dog. This proves to be a code leading to the source of the pensions but Keller abducts Caroline before she can get there.
Caroline's friend Irena is swindled out of the possession of a twelfth century icon by Alan Sutherland, a suave con-man who preys on women. Caroline buys back the icon at an auction and, joined by Harry posing as a millionaire, they devise a con trick of their own to play on Sullivan, which involves his putting up eighty five thousand pounds of his own for possession of a supposedly priceless ring.
Whilst being engaged to protect Frank Dilling, a vital witness in a corruption case, Harry and Caroline are involved in a car crash. Harry wakes up in hospital, where he visited by a police inspector, who asks him about Dilling's location so that the police may guard him. However the whole situation has been manufactured and the man is a bogus cop, anxious to silence Dilling and Harry must go after him and stop him.
Harry is the target of a failed assassination attempt by Kate Lindermann, whose gangster father he helped bring to justice and who died in prison. She believes her father was innocent and that Harry framed him. In order for her to learn the truth, Harry arranges for Kate to meet two former associates of her father, only to discover that the so-called attempt on his life was a set-up and he has been led into a trap.
The Protectors are assigned to locate Professor Schelpin, a scientist who has defected from Russia to the West. In fact he surfaces at a conference where he declares his intention to demonstrate the evils of germ warfare, before disappearing again. The Protectors discover that he has a phial of germ warfare toxin, which he plans to release on the anniversary of the Hiroshima bombing and must be stopped.
Paul is taken prisoner by a crook named Charlie, who connects him to a time bomb, which he will detonate unless Harry and Caroline steal a consignment of valuable jewels for which they are acting as couriers. A reluctant Harry makes the switch of the packet of jewels but, arriving at Paul's prison, finds Charlie dead and the bomb still ticking.
On the trail of runaway Susan Crediton, the Protectors find that she is involved in a strange numbers game, taking down the registration plate numbers of cars, one of which is owned by Laurence Savage, a noted heart surgeon. The cars are used to smuggle heroin and, after trailing Savage, Harry arrives in Spain to confront the boss of the organization.