Nick Cheung portrays real estate agent Hong Siu Lung, who was dumped by his greedy fiancé when the house he gave her was too small. One day, he comes across an ad about a cheap penthouse on sale. Wanting to purchase the house and then resell it for a higher price, he strikes a deal with three others – Kam Fung (Sammi Cheng), a wealthy divorcee; Ah Hak (Angelababy), Hong Siu Lung’s stepdaughter; and Very (Oho), a wealthy college graduate from mainland China, convincing them to split the purchase with him. When the estate market fell, the four are forced to live together.
Chan Wing Yan, a young police officer, has been sent undercover as a mole in the local mafia. Lau Kin Ming, a young mafia member, infiltrates the police force. Years later, their older counterparts, Chen Wing Yan and Inspector Lau Kin Ming, respectively, race against time to expose the mole within their midst.