Two unsigned personal invitations will bring the titled Englishman, Lord Brett Sinclair and the self-made oil tycoon, the American Danny Wilde to Monaco for an encounter with a stunning brunette and the Mediterranean crime syndicate.
Brett and Danny find themselves engaged in a cat-and-mouse game of deceit and murder as a long-missing heir returns from the grave claiming a several-million-pound fortune. Is he a sibling or an impostor?
Knocked unconscious after a staged road block, Brett awakes in a fake hospital, from which he eventually escapes, to be told by Danny that he has a double who has been impersonating him. Reclusive millionaire Sam Milford is due in town and Brett is one of the few people he trusts to come near him. Danny reasons that the double is out to kill Sam but then realises that there is no double and Brett himself was programmed to kill whilst in hospital.
Once again, Danny's life is in grave danger as a newspaper photograph showing him carrying a case with a statuette of a German eagle will attract the attention of an ex-Nazi fanatical Count and his assassins.
Angie is an old male friend of Danny's from the days before he struck it rich and Danny finds it hard to believe that Angie, re-encountered on the French Riviera, is now a hitman paid to rub out a witness against corruption in big business. Despite Brett's warnings of caution Danny is prepared to champion Angie but this leads to a showdown between the two old friends, which only one can survive.
Things turn volatile when unexpectedly, Danny gets himself handcuffed to a much-wanted attaché case, sparking a relentless manhunt from both MI6 and Iron Curtain agents who need to recover the case at all costs.
Thaddeus Krane is a ruthless millionaire who has made his wealth from the sufferings of others and his young secretary Cliff aims to expose him by contacting Brett. However Cliff is killed and Brett abducted and whisked away so that Krane's henchmen can ascertain how much he knows. To confuse Krane Judge Fulton persuades Danny to impersonate Brett, and all is going well until a lady friend of Brett's almost ruins the situation with her curiosity.
Brett and Danny accidentally discover a plane wreckage, and with it, a low-cost, high-grade synthetic fuel formula, which attracts a parade of oil tycoons and "considerate" daughters, all claiming the formula.
Danny is mistaken for Lomax, an international criminal, and taken to meet Mitchell, who has engaged Lomax to master-mind a plot to rob an American air force base of a huge amount of gold bullion. Learning of his friend's plight, Brett poses as the gang's getaway pilot but the game seems to be up when the real Lomax arrives. Can the Persuaders rely on female gang member Charlie to save them?
Judge Fulton charges Danny and Brett to get former gangster Frank Rocco from Italy to America to testify against a large crime syndicate. They must evade both the police and Torino, a rival mobster out to silence Rocco. Accompanied by photo-journalist Sidonie, the party eludes the police but are forced to take shelter in a villa owned by wealthy Count Sangallo, who is in alliance with Torino and is about to deliver them to him.
Whilst Danny is on a date with Lisa Zorakin, spoilt daughter of a millionaire, the girl is abducted. Zorakin suspects that Danny is involved but in fact Lisa is a willing captive, her kidnapper being Michel, her lover, and the plan is to extract a 'ransom' to set them up together. Danny agrees to investigate on behalf of Zorakin to clear his name but further complications are provided by Lisa's long-suffering companion Mary, who also wants a share.
Brett attends the funeral of his uncle Randolph, where his cousin Kate, a crime novelist, tells him that she believes he was murdered. Brett is not convinced but then six more members of the Sinclair family are all bumped off, as well as the family undertaker. It becomes apparent, however, that one of the dead men is not dead after all when he traps Kate and Danny in the family vault. It is down to Brett to rescue them.
The Persuaders are called in to assist the Grand Duchess Ozerov, an elderly Russian former aristocrat. There is contention as to the rightful owner of her jewels, kept in a Swiss bank. The Russian government is one claimant and her nephew Sergei another, in addition to the duchess herself. Brett and Danny are to go to the Russian village where there is proof of her marriage to Prince Ozerov and, consequently, her right to own the jewels. However two men in the pay of Sergei are out to stop them.
Wealthy Shelley Masterson is being courted for her money by the suave Foster, who is being backed by gangster Coady and Brett and Danny vie for her affections to save her, particularly as she has signed a document leaving everything to Foster should she die. To help her they give her money with which to pay off Foster, only to find that they have been duped. She is not a victim but a confidence trickster herself.
After Brett enters his car for a motor race, attempts are made on his life. A man called Vine approaches him, asking him to throw the race. He is working for Louise Cornell, head of a race fixing gang but she denies any allegations of trying to kill him - she just bribes people to lose. Could the would-be assassin be Jenkins, a former racer who, after an incident years earlier where he tried to overtake Brett, leading to an accident which incapacitated him, was never able to drive again?