A retired judge who regrets those criminals he had to let get away arranges for Brett and Danny to meet, and then gets them arrested so that they have the choice of either helping him out in his fight against crime or staying in jail. Their first assignment is to locate an heiress by her heart-shaped birthmark.
Mission: Monte Carlo is a "movie" comprised of two episodes from the 1971 British/US TV series The Persuaders - which accounts for the presence of Basil Dearden, who died that year. The only element that the two hour-long episodes truly have in common is their setting: Southern France's Cote D'Azur. The discovery of an exotic dancer's corpse leads playboy secret agents Danny Wilde (Tony Curtis) and Lord Brett Sinclair (Roger Moore) on a merry chase after a gang of stock swindlers. This storyline is expanded with scenes from a second Riviera-based Persuaders installment, written by Val Guest, wherein Wilde and Sinclair pursue a contingent of gold smugglers.
Life is never dull where Lord Brett Sinclair and Danny Wilde are concerned. But who would expect dire danger, hilarious though it may be, to face them in one of Brett's baronial homes? Even more unexpectedly, murder and black magic take place when Danny decides to own his own little piece of England and buys a tumble down old cottage. The old mansion, Greensleeves, has been in the Sinclair family for generations, but has been unoccupied for a long time except for an aged butler named Moorehead. It is only by chance that Brett discovers that it has been restored without his permission. He and Danny decide to investigate and, entering through a secret tunnel, find a letter addressed to a theatrical agent asking him to an actor who resembles Brett. Brett promptly poses as the actor and gets the job of impersonating himself. Danny and Brett have a lot to overcome before Danny can enjoy his little piece of England!