In London, the esteemed Sir Charles Braithwaite, the Commissioner for Scotland Yard, finds himself in a daunting battle against a European organized crime syndicate responsible for a series of daring robberies. To aid in this complex investigation, the British Prime Minister, amid rising public scrutiny, calls for external assistance, a move perceived as an affront by the local press. Enter French Inspector Jacques Clouseau, sent to lend a hand in untangling this web of crime.
Upon his arrival, Sir Charles briefs Clouseau, highlighting three suspects currently detained. Among them, Addison Steele remains in custody, while Frenchie LeBec and Steven Frey have managed to evade capture. Sir Charles cautions Clouseau to remain vigilant, as he suspects a traitor lurking within their ranks. Meanwhile, Steele, who operates as the prison's barber, provides Clouseau with crucial information about the elusive gang leader, known only as "Johnny Rainbow." However, Steele cunningly uses chloroform during a shave, leading to his own escape.
At Scotland Yard, Superintendent Weaver equips Clouseau with a range of experimental disguised weapons to aid his quest for justice. During an encounter with Frenchie, who attempts to take Clouseau's life, a chaotic turn of events results in Clouseau unintentionally killing him instead, much to Sir Charles's chagrin. The ensuing investigation leads Clouseau to a matchbook linking Frenchie to the Tudor Arms Inn. Once there, Clouseau's encounter with two women leads to his abduction, resulting in a bizarre scenario where a rubber mold is made of his face.
His investigation takes a dark turn when he discovers a tattoo on the inn's owner that is connected to "Johnny Rainbow." Following the clues, he attends Frenchie's funeral in France, only to be ambushed by the gang. Fortunately, Lisa Morell, Weaver's maid, intervenes just in time, revealing that she is an undercover Interpol agent sent to assist him. Initially skeptical, Clouseau arrests her, only to later be informed by Préfet de Police Geffrion of her authenticity.
The story unfolds further as Clouseau infiltrates the gang's hideout, unveiling the shocking truth that Clyde Hargreaves is, in fact, Johnny Rainbow. He discovers that the gang intends to execute a heist involving thirteen Swiss banks, framing Clouseau in the process. Clouseau learns of their plan and sets out for the hideout but is soon pursued by Rainbow's henchmen, only to be saved by Weaver—who is secretly the mole among them—who slyly slips a train ticket into Clouseau’s pocket.
On a train journey to Zurich, Weaver tries to eliminate Clouseau while impersonating him. The plot thickens when Lisa is kidnapped, putting Clouseau in an even more precarious position. Weaver, alongside Rainbow, misleads the Swiss authorities, orchestrating the transfer of stolen funds disguised as chocolates, cleverly utilizing a Lindt factory as their cover.
In a twisted climax, Clouseau finds himself arrested as the real culprit behind the robberies. However, when Weaver’s disguise as Clouseau leads to his downfall, it becomes clear that Clouseau is innocent. Determined to save Lisa, Clouseau confronts Steele and ultimately escapes, thwarting the gang's elaborate heist and sinking the ship full of stolen money. Despite the chaos, Rainbow and his crew manage to escape unscathed, while Clouseau triumphantly returns to France, bidding farewell to a grateful Sir Charles.
