Poison enlists his friends to stage an attack on Rich Chan, [Cheung Ying], in order to create the illusion of a heroic rescue. This clever ruse is designed to establish Poison as Rich Chan's new bodyguard, a role he hopes will lead to more lucrative opportunities. Meanwhile, Rich Chan decides to hire Dragon, [Lee Hoi-Sang], from the Courageous Dragon Detective Agency, to deliver three valuable diamonds, setting into motion a series of events filled with deception and unexpected twists.
Poison and Dragon, who initially appear to be mere conmen, soon recognize each other as rivals, each threatening to expose the other's secrets to their new boss. This recognition sparks a tense rivalry, adding complexity to their relationship. After Dragon successfully delivers the diamonds, he is unexpectedly kidnapped by Mary [Angie Chiu Nga-Chi] and her associates, revealing the dangerous world they are entangled in.
The plot thickens as Poison fights off Mary's men and Ping, a man hired by Rich Chan to eliminate Dragon. During this chaos, Poison and Dragon engage in a fierce fight over the gemstones, which are accidentally dropped onto the street and crushed by a steamroller. To their dismay, they discover that the diamonds are actually fake, revealing that Rich Chan has set them up from the very beginning.
Realizing they've been duped, Poison and Dragon team up to help Mary, whose adoptive father, Uncle [Yue Ming], has been swindled out of his money and precious family diamonds by Rich Chan. Using Dragon's detective gadgets, they sneak inside Rich Chan's residence and find out that he keeps the real diamonds concealed around his neck at all times.
In a daring move, Poison lowers Dragon into Rich Chan's bedroom using a rope, aiming to steal the diamonds. However, they get caught when Rich Chan wakes up from the sweat from Poison's body dripping onto him. This force them to retreat quickly, but their plan isn't over. Dragon then calls Rich Chan, pretending to be Liu Fu, a gemologist, and claims that he has the real diamonds. Dragon successfully swaps the genuine diamonds with fakes during an examination staged by Liu Fu, and then demands a ransom of HK$2 million for the return of the authentic stones.
At their exchange, Poison and Dragon steal the money and escape on a motorcycle, returning the real diamonds to Uncle and Mary. However, they soon realize the money they received is counterfeit. Despite this setback, Uncle generously shares his diamonds with Poison and Mary, symbolizing their victory over the deceptive Rich Chan and their newfound alliance.
Throughout this tangled web of schemes and double-crosses, the film explores themes of cunning, loyalty, and justice, all woven into a humorous and action-packed storyline that keeps viewers guessing until the very end.
