Plot

Thongs and Octopus accept a job from their landlord: kidnap a baby. Soon, the baby awakens strong paternal feelings in the two crooks, leading to complications when it comes to handing him over to his possibly crazy gang boss grandfather.

For never-do-well compulsive gambler Fong, there's only one thing more fearsome than debtors at his doorstep - having to coax a crying baby. But what if the baby becomes his golden goose to fend off his debtors? Can he overcome his phobia of diapers, milk bottles, and cloying lullabies?—Invisible Man

Friends Thongs and Octopus evade security guards in a hospital, having stolen money and cancer medication from the safe. Meanwhile, a newborn baby to the wealthy Lee family is snatched by Max, the mother's ex-boyfriend, prompting the security guards give chase, ignoring the burglars, and corner Max on an escalator. Following a violent struggle, Max and the baby fall over the side-the baby is caught by Thongs, while Max plummets to his death. While the guards are distracted, Thongs and Octopus leave in the Landlord's minivan.

A few months later, the Landlord finds his flat burgled, his life savings gone. He receives a phone call from his middleman Uncle Seven, offering him a job to kidnap baby Lee on behalf of a triad boss, who claims the baby is his grandson. Enticed by the HK$7 million reward, Thongs and Octopus accept the job without knowing its objectives, finding out only after the Landlord has fled the Lees' mansion with the baby. Disgusted by the idea of kidnapping a baby, Thongs threatens to return him, but relents after the Landlord tells him of his predicament. En route to their rendezvous point in Sai Kung, the trio encounter a police road block which the Landlord attempts to outrun, only to crash his van down a hill. As the police close in on them, the stuck Landlord instructs Thongs and Octopus to leave with the baby. While in custody for reckless driving, the Landlord learns of the baby's value through the news. He phones Thongs, instructing him not to hand the baby over to anyone prior to his release so he can jack up the price. Over the next few days, Thongs and Octopus take care of the baby, developing a strong bond with him. The two begin to regret their vices: Thongs resists the urge to gamble, while Octopus feels sorry for cheating on his wife. Meanwhile, both the triads and the police are after the baby. The triad boss, enraged by the non-delivery of his "grandson", sends his men to retrieve the baby from Thongs' flat. Confronted by both the triads and Police Inspector Mok, Thongs and Octopus go into hiding with the baby.

Shortly after his release, the Landlord is brought to the triad boss, who increases his offer to HK$30 million for the baby. He finds Thongs and Octopus at the hospital, where the baby is being treated for fever. The Landlord informs the two of the triads' latest offer, but Thongs and Octopus are more concerned about the baby's welfare than the cash. However, the two agree to bring the baby to the triad boss' mansion, where the Landlord will meet them with the rest of the money. They reach the triad boss' mansion and hand over the baby reluctantly. As the trio are about to leave, they hear the baby crying for them as a blood sample is taken from his arm. Thongs and Octopus experience a flashback of the days they spent with the baby. Overcome by their feelings, they fight their way into the triad boss' private amusement park to recover the baby while the Landlord leaves with the money. Thongs almost manages to escape with the baby, but is forced to surrender when the triads threaten to hurl Octopus to his death.

Thongs and Octopus are taken to the triad boss, who insists the baby is his grandson, only to be proven wrong by the blood test. Driven mad, the boss places the baby in a deep freeze room next to Max's corpse so the baby can be with his son, prompting Thongs and Octopus to fight for the baby. The two end up trapped in the room with two minions, but are saved when Inspector Mok arrives with the Landlord, who swiftly cracks the lock to the room. Thongs and Octopus run to the garage with the comatose baby, where Thongs attempts to revive him with a makeshift defibrillator powered by a car battery from a Pagani Zonda by holding onto the crocodile clips with his bare hands. Despite his efforts, the baby does not come to and is driven off in an ambulance, where his heart is found to be beating weakly. Imprisoned for kidnapping, Thongs, Octopus and the Landlord volunteer for a mock capital punishment demonstration during an open day, using the opportunity to apologise to their loved ones. After the demonstration, Inspector Mok informs the three that their sentences have been further reduced by the Department of Justice. Thongs, Octopus, and the Landlord then see the baby alive and well with his parents. As a token of appreciation for saving the baby's life, Thongs, Octopus and the Landlord are offered jobs by the Lee family as a bodyguard, chauffeur and head of security respectively.