The core gameplay of Sleeping Dogs consists of giving the player an open world environment in which to move around.
After learning of Dogeyes' attack on the Golden Koi, Winston takes the offensive by attacking one of Dogeyes' warehouses. However, doing so will displease the Chairman and Dragon Head of the Sun On Yee, Uncle Po. Wei convinces Winston to spare Dogeyes' drug maker Siu Wah and give Uncle Po a bigger profit than what the Jade Gang offers. Wei successfully does so and fully earns the trust of the Water Street Gang. When Winston is contacted by Uncle Po, who wishes to meet with Wei, he relays the meeting to Raymond, who is concerned that Wei is becoming "one of them". However, Raymond relents as Wei has gotten ever closer to infiltrating the Sun On Yee. During Winston and his fiancée Peggy Li's wedding day, the Sun On Yee is attacked by a rival Hong Kong Triad gang, the "18K". Amidst the fighting, Winston and Peggy are shot dead and Uncle Po is critically wounded, but Wei manages to get him to the hospital. For saving his life, Uncle Po promotes Wei to the rank of red pole and succeeds Winston as leader of the Water Street Gang. At the request of Winston's mother, Mrs. Chu, Wei captures a member of the 18K called Johnny Ratface. Johnny confesses that Dogeyes was behind the attack as he is tortured to death by Mrs. Chu. Wei captures Dogeyes, whom she also kills and dismembers.
When fellow Sun On Yee red pole Henry "Big Smile" Lee threatens to take the Water Street Gang's territory, Wei refuses and Lee's henchmen unsuccessfully intimidate Wei. However, he agrees to an alliance with red pole "Broken Nose" Jiang to prevent Lee from achieving his goals. During a meeting with other red poles and a hospitalized Uncle Po, a temporary Chairman must be elected. Jiang suggests Po's nephew "Two Chin" Tsao, to avoid Lee nominating himself. On Jiang's request, Wei sabotages Tsao's residence to make him appear incompetent to lead, making the position of Chairman limited to Lee and Jiang. When Uncle Po suddenly dies, Wei is told by Pendrew his undercover duties are over, though he protests: if Lee becomes the Dragon Head, the Sun On Yee will be worse than it was under Uncle Po.
Furious at Wei's insubordination, Pendrew leaks information about his undercover operations to Lee, who orders Jackie's kidnapping in order to lure out Wei. Although Wei frees Jackie, Jackie is once again kidnapped and killed by the 18K. Captured and tortured, Wei manages to escape and sets out to assassinate Lee, slaughtering his men. After a long arduous chase, Wei corners Lee and kills him by shoving him headfirst into an ice chipper, grinding the upper half of his body into pieces. Raymond congratulates Wei on a case well done, but informs him that Pendrew has been promoted to Interpol and cannot be touched.
The following day Wei receives a package from Jiang. Although the package is addressed to Officer Shen, revealing her knowledge of his undercover activity, it contains a video of Pendrew killing Uncle Po at the hospital. Po reveals that he had made a deal with Pendrew in the past to further his career in exchange for allowing the Sun On Yee to continue operating, but Pendrew admits that Po has outlived his usefulness to him. With this incriminating evidence, Wei throws Pendrew into jail, knowing he will not survive long in a place filled with Triad members he has put away throughout his former career.
Jiang is later seen monitoring Wei as he is conversing with Teng. She tells her triads to leave Wei alone as he has proved his loyalty to her, "one way or another".