The film follows the comic yet sharp-edged misadventures of Mannix Private Detective Agency in Hong Kong, a small-time outfit guided by private detective Wong Yeuk-sze [Michael Hui] and his emotionally drained assistant Puffy [Ricky Hui Koon-Ying]. A would-be recruit named Lee Kwok-kit [Sam Hui], a kung fu enthusiast chopping through life at a Vitasoy plant, drifts toward the agency after a series of personal misfires—his flashy tricks barely impress Wong, who remains skeptical of his usefulness. The turning point comes in a kitchen confrontation when a wallet goes missing and a bystander is unfairly blamed. In a flurry of chaos, Wong fights with improvised sausage nunchaku, but Lee unexpectedly steps in to recover the wallet. It seems to prove Lee’s merit, and Wong hires him, though the wallet’s whereabouts reveal a sly twist: it had been in Wong’s possession all along, and the scene exposes a petty sting that undercuts the initial bravado.
Together, the trio dives into a string of varied assignments that showcase their mismatched but complementary talents. A client woman asks them to snap proof of her husband’s affair so she can claim a court reward, testing their ability to navigate relationships and leverage delicate information. Soon after, a supermarket owner enlists them to thwart a planned shoplifting operation, pushing Lee to deploy his kung fu skill in a high-stakes confrontation with the thugs. The balance between luck, wit, and fistwork is a constant in their working style, and the agency begins to feel like a living, breathing organism that thrives on chaos and clever improvisation.
The film builds to a defining squeeze of danger as a gang of robbers led by Uncle Nine [Sek Kin] begins to terrorize a cinema mogul and his patrons, turning public spaces into arenas of risk. Wong becomes one of the targets, sustaining a leg injury in the melee, while Lee fights back, catching a handful of the gang and delivering decisive blows. The criminals flee in an ice-cream truck that one thug had stolen, only to be corralled when Lee drives the fugitives toward the police station. The situation culminates as Lee activates a freezer mechanism to immobilize the gang inside the truck. At the station, a Police Sergeant [Richard Ng Yiu-Hon] oversees the aftermath, and Lee and Wong eventually hand the culprits over, marking a temporary victory for the duo even as the wider world remains precarious.
Months pass, and Wong returns alone to a suddenly changed landscape: his agency is quiet, his former clients gone, and Lee’s Cannon Detective Service has eclipsed his own operation. A tense bargaining moment follows as Lee proposes a partnership, offering Wong a larger share of profits. Wong initially refuses but ends up learning a sly snatching trick from Lee, a trick that had already been deployed earlier in the film. The two men finally strike a pragmatic deal—an equal partnership where both share the gains—an ending that hints at reconciliation and renewed competition rather than absolute triumph. Puffy, too, finds a new path beside Lee, completing a volatile but effective trio that redefines what a small detective agency can accomplish in a city where danger and humor walk hand in hand.
