Year of the Snake takes place immediately after the original story of Sleeping Dogs. Wei Shen starts doing normal police work again, but is initially given punishment duty as a beat cop due to the carnage caused in the main storyline. However, Wei almost immediately encounters a cult that is doing their best to usher in the apocalypse with a bang during Hong Kong's New Year celebrations. The DLC is 12 missions long and gives Wei the ability to tase and arrest opponents in combat. Like the Nightmare in North Point DLC, Year of the Snake is accessed from the main menu and played separately from the main game.
It begins when Wei is at the police station with Inspector Teng, where she tells Wei that the bosses were unhappy with his recklessness when he infiltrated the Triads back then, due to the numerous damages caused to civilians and infrastructure. Wei found himself to be an ordinary police officer. One night, when Wei was about to issue a ticket to a sports car, a suspicious-looking blue Enterprise ran into the district and drew his attention. Wei reported the incident to the dispatch and immediately gave chase, which the dispatch found to be a rented car. The car stopped near a dragon dance attraction, where Wei asked people around about men in yellow shirts. Wei quickly apprehends the suspects and made his way to the blue sedan, which turned out to be armed with a bomb. He quickly ditches the car into the ocean despite the dispatch's request to stay put. Wei then asks for the address of the car owner and found that it was a warehouse. Upon inspecting the warehouse, he found bomb manuals and bomb parts, as well as signs of a cult. Before he could leave the area, he was ambushed by cultists but was able to handle it due to the arrival of a few fellow officers. Back at HQ, Wei interrogated one of the cultists and found out that the cult predicted an apocalypse when the Chinese New Year started.
Continuing the investigation, Wei went to Aspirazone to get his undercover outfit and made his way to K-Bar in Central, and overhears many conversations there, including a conversation about bomb trading. After overhearing the conversations, Wei went to the back room and found the dealer, who escaped from the building, only to find himself surrounded by police in the end. Wei arrested the dealer and put him into the cruiser, where the dealer told that he only sold one bomb and about to set it off at a certain place when there are many people. On his way to Mobile HQ, the cruiser was ambushed by a group of people in Neo V.
After reaching the Mobile HQ, an officer told Wei that there were bomb threats at a crowded shopping center and went there to investigate. Wei found the cultists who were about to set a bomb hidden in a sports bag and quickly dispersed the crowd. After fighting the cultists, Wei brought the bag of bomb to the bomb disposal unit across the street. Next, he made his way to meet the cultist bomber. The bomber ran away, and inadvertently hit the timer. Wei, however, managed to ran away from the bomber, who blew himself into pieces. Then, he went to a parking lot (where there was a bomb threat) and investigated some of the vehicles, where he found an 860 MHC sports car that ran away. Wei chased the car with the police bike and hijacked it, only to found out that the sports car was rigged with a bomb, where Wei ditched the car into the ocean.
After ditching the car, Wei received a report about a mini bus bombing in Central. To prevent further catastrophe, Wei made his way to the North Point Bus Depot, where he saw the cultists about to rig a bus with their car bomb. Then, Wei told Inspector Teng about a suspicious truck activity sourced from the fish market. In the fish market, Wei encountered the cultists again, and this time, managed to found the bomb maker, who was scared because the cultists abused him and told Wei to protect him. On the way to the Mobile HQ, Wei was ambushed again, but managed to make it to the HQ. After that, the dispatch told Wei that there was a riot in Soho and told Wei to go to the mobile HQ to receive equipment upgrades. Now, working with the SWAT, Wei made his way through the riots and dispersed the rioting crowds (and also fighting the cultists). After taking care of the riot at Soho, Wei made his way to the Plaza, now armed with tear gas grenade. Unfortunately though, the cultists are wearing gas masks now, so Wei's tear gas explosions doesn't affect them. Nearby the Plaza, the crowd was shocked by an out-of-control Bisai, which ran into people on the staircases. At the Plaza, the riots are quite intense, making it rather difficult for Wei to disperse the crowds.
The cultists are getting even worse now, as the dispatch reported that there was a van carrying nerve gas. Riding shotgun in a Supercharged Police Cruiser, Wei tried to fend off the ambush vehicle while a fellow police officer drove the police car. The duo then went separate ways: Wei takes care of the escaping Master while the police officer takes care of the van.
Wei, now in Aberdeen, confronts the cultists at the docks. Both sides are now engaged in a long gunfight. After finishing the cultists at the docks, Wei made his way to Central to another gunfight, now occurring in a park, where Wei and fellow SWAT officers managed to finish the gunfight. Then, Wei, along with Inspector Teng and a fellow officer went to the docks to finish the cultists by using a police boat. After protecting the police boat from the cultists, Wei was dropped at a barge to encounter another wave of armed cultists and the Master himself. In the end, Teng wanted to put the Master under arrest as soon as possible, but Wei held off the arrest so he could first demonstrate that the Apocalpyse the Master prophesized would not occur. At precisely midnight, Wei officially put the Master under arrest as fireworks celebrated the New Year, ending the cult's quest to terrorize Hong Kong.
- The name of the DLC gets its name according to the Chinese Zodiac calendar as 2013 is the Year of the Snake.