The Protectors are approached by Laura Sutton, who is afraid that her brother Jimmy has been recruited to work for Quin, an internationally known ruthless mercenary whose only concern is money. Harry travels to Spain in search of Quin and ends up in a face to face confrontation with him.
The Protectors are in Copenhagen, where their services are required by a wealthy widow, Madame Andersen. Her young daughter Eva has been kidnapped and is being held to ransom in a disused fort. Harry agrees to act as the bagman and delivers the ransom to the abductors. However, things do not go according to plan.
In Venice there has been a daring robbery, the spoils being a priceless art collection. The Protectors learn that the robbers are a terrorist gang who aim to sell their prize to the highest bidder in order to buy armaments for their cause. Helped by the river police Harry determines to thwart the gang.
Irena Gayevska is a young Russian scientist who is anxious to defect to the West and to marry her boyfriend there. Because of her skills she is a valuable defector and the Protectors are assigned to smuggle her over the border. Inevitably her absence is detected, leading to a pursuit by the Soviet forces.
Following a jewel theft in Denmark, a con artist named Bergen is responsible for double-crossing a number of people. The swindled parties want revenge and seize Bergen's daughter, Kate, who is unaware of what has been happening and has played no part in the heist itself. The Protectors are engaged to rescue her but Caroline is also endangered.
The Protectors are hired to combat industrial espionage after it becomes apparent that somebody is leaking information from a cleaning products factory. All the necessary precautions are put into play but nevertheless information from boardroom meetings is still getting out, pointing to an employee as the culprit. Harry decides to set a trap to hoist the traitor with their own petard.
Caroline undertakes a solo assignment on behalf of wealthy Cedric Parton. His son Caspar is living in Venice and is making a number of very considerable withdrawals from his bank account, all of which are in favour of somebody called George Milworth. On the face of it it would appear that Cedric is being blackmailed by George but when Caroline arrives, there is no George to be seen and the motive turns out to be wholly different.
Monica Davies is cut out of her father's will for her behaviour and sends him a letter to say that she is about to come into a large amount of money nevertheless. The trail leads the Protectors to Austria where Monica is involved in a kidnap plot whereby a number of skiers are unknowingly held to ransom at the top of a mountain and the authorities are only able to guess the terrorist's identity from their voice.
The holidaymakers are released after the ransom is paid and the Protectors join forces with Inspector Luhrs to try and work out which of the people in the party may have been involved in the terrorist group. Having done this they also have to find the possible link with Monica's letter and the extent of her involvement.
The poorly Mrs. Douglas enlists the aid of the Protectors after her young son Stephen is caught apparently smuggling a large amount of drugs in his back pack. When Harry goes to see Stephen in a Spanish jail the boy refuses to help himself but Harry is convinced that he is under the influence of Raphael Santana, the real drugs baron, and sets out to prove the link between the two.
A dissident Russian author is smuggled out of Russia into Britain, along with the manuscript of his book, which is severely critical of the Communists' political regime. Harry is hired to look after him but a pro-Communist group, anxious to burn the manuscript, come after and capture both men, requiring the intervention of Caroline and Paul.
Harry is amazed when an old friend of his whom he had assumed to be dead turns up in London. The man's 'death' was actually staged and is linked to a complicated and lucrative insurance fraud. This, in turn, leads Harry and Caroline to Venice, where the man is killed, this time for real. He has, however, left behind a letter which the Protectors must understand to scupper the deadly scam.
The Protectors are hired by the Hungarian actress Ilona Tabori, who wants them to help her take her father's body through the Iron Curtain and back to his natal village, where it was his wish that he should be buried. The funeral is successfully accomplished but Harry has had misgivings about this assignment all along and he could be proved right as it transpires that Ilona has another agenda to the one for which she first hired them.
Harry is pleased to meet up again with an old college friend of his, Zeke, who is playing jazz piano in a local night club. Unfortunately Harry is unaware that Zeke's sudden re-entry back into his life is no coincidence. In actual fact Zeke is being blackmailed by mobsters with whom he has got into debt into setting Harry up as a target for his enemies. Will Zeke be able to go through with it or will he save his old friend from his fate?
In Venice the Protectors come to the aid of an old friend of Caroline, Lena Hayden, an investigative journalist. She has reason to believe that a supposedly respectable local politician was actually involved in a murder. Her suspicions place her life in danger and require the Protectors to seek out a man who is believed to be long dead to assist her case.
In Spain, young David Mitchell, son of a wealthy man, has joined an extreme revolutionary group and taken as a hostage Anna De Santos, a childhood friend. The group intend to blow up a bridge as an American diplomat passes over it. The Protectors are alerted and Harry masquerades as an explosives expert supposedly about to assist the group with their plan in order to infiltrate them.
In the heart of the Home Counties business man Sir Charles Standish receives kidnap threats against his teen-aged daughter Vicky, possibly by aggrieved former business associates. Rather than involve the police and panic Vicky, Standish engages the Protectors but things must look as normal as possible and so Harry is passed off as her new tutor though he does not have the easiest of times with her.
Wealthy Canadian Adam Ferris gets in touch with the Protectors when his heiress daughter Anne goes missing in London and turns up again having joined a religious sect with sinister overtones of the occult. Ferris is concerned that the group will brain-wash her into giving them her considerable inheritance. Harry poses as a reforming alcoholic in need of spiritual guidance in order to join the sect.
Caroline is asked by British Intelligence to act as a 'goat' to act as decoy to catch a 'tiger'. An ex-boyfriend of hers is a spy and she is told that he is the potential victim of an assassination plot, which she is brought in to foil. However, when the man tells her that he has resigned as an agent, Caroline sees that she has been employed under false pretences. She is indeed a decoy and only Paul can save her.
Harry is on the trail of one of the largest heroin smuggling operations, a trail which leads him from London to Denmark where he comes to on a landfill site to discover that the gang involved in the smuggling has eluded him. However he is aware of the harbour port where the drugs are being stashed and, as he is the only man apart from the miscreants, who knows its location, it puts him very much in danger.
Anne Gordon seeks the help of the Protectors. Her son John is on trial for a crime that he did not commit though her fears are actually for her husband Arthur. He is a disturbed mental patient who has gone missing after hearing about the trial. The judge in charge of John's case is Judge Cronin and the Protectors must prevent Arthur from killing him.
Harry is on a train returning from Edinburgh to London. He gets into conversation with a fellow traveller. This man is the poetic Shadbolt, but there is something about him that Harry cannot possibly know. Shadbolt is also a professional assassin and his presence on the train is no coincidence. He has been paid to kill Harry at a given time, a fact to which Harry must tumble for the ultimate show-down.
Carrie Blaine is a professional singer about to make her come-back. However she is convinced that her house is haunted when the clocks start to run backwards and she keeps hearing a chorus of children singing 'A Pocketful of Posies'. Is she correct in her guess or is she about to have a break-down? Or is she being used as part of a sinister plot by one of her associates? Enter the Protectors to find out.
Harry joins a car rally as a driver whilst the Protectors are in pursuit of their toughest case to date. A Swiss bank hires them to go after stolen papers but they only want the copies, not the originals. This involves cracking a safe, photographing the contents of a locked brief-case - the details of a numbered bank account - and returning them to the bank without the account holder knowing that anything has happened.
All the copies of a film have been stolen at the pre-production stage and Harry is called in by its director to try and recover them. Whilst they are talking in his office, they are joined by the alleged thief, who offers to return the prints in exchange for a ransom. The money is duly paid and the blackmailer steps into the lift. However, he is not seen to get out again, or to leave the building. How did he vanish into thin air?
A gang of hi-jackers led by villains Birch and Slater are making off with security vans containing consignments of platinum in different European locations and the Protectors are called in to stop them. However the assignment is no easy task as the evidence, namely the vehicles containing the booty, seem to disappear. Could an old chemistry set experiment hold a clue as to what is happening?