Plot
One night in a parking lot in Shanghai, a man named Wu Yanzhen was killed by hitman Zhou Quan, known as Mr. Z, after Wu made a call to his lover Zeng Jiurong, which was filmed by a civilian. On the other hand, a down-to-luck extra actor Chen Xiaomeng, who is broke and massively indebt gets almost hangs himself but halts when his phone rings. Xiaomeng then finds a coupon for a bathhouse and proceeds there while Quan also enters the same bathhouse while driving away from a police road block which turns out to be a filming set. When Xiaomeng is denied entry due to the coupon expiring by midnight, Quan helps him and the latter thanks him, but Quan ignores him. When Xiaomeng was showering, his soap bar slips out of his hand which Quan steps on and falls unconscious on the back of his head. Xiaomeng then takes Quan's locker key while placing his own next to Quan and leaves with Quan's belongings and car, where Xiaomeng finds an abundance of cash and uses it to pay off his debts as well as his ex-girlfriend who is about to get married.
Xiaomeng then visits Quan in the hospital to return his belongings but he discovers Quan has become amnesiac and Quan thinks he is Xiaomeng, so Xiaomeng decides to take on Quan's identity to enjoy a luxurious life, but he pays for Quan's hospital bills. On the other hand, author and media company CEO Li Xiang, who is a single mother, arrives to the hospital as her 12-year-old son, You, collapsed on physical education class. You tells his mother he is stressed preparing a speech about his father, whom he tells everyone that he is an astronaut.
While leaving the hospital, Xiang drives on a pudding which splashes on Quan so she offers him a ride to Xiaomeng's apartment address, which he thinks is his home. As Xiaomeng owes rent to his landlord, the landlord tries to kick Quan out but Xiang helps him pay rent. Seeing the rope that Xiaomeng used to hang himself, Quan deduces that he had suicidal thoughts and Xiang encourages him to scrap those thoughts. While cleaning up Xiaomeng's apartment, Quan finds items which define Xiaomeng's characteristics and thinks that they are his own, which he marks down on a notebook. Quan also takes up Xiaomeng's career as an extra actor and shows up to work on film sets.
Meanwhile, Xiaomeng accesses Quan's luxurious apartment and lives the time of his life. He then finds different identities and outfits of different professions,bad well as a pistol in his closet before receiving a phone call meant for Quan to receive CN¥200,000 payment for a previous killing job. Xiaomeng later bumps into Quan, who invites him and Xiang to his apartment, where Xiaomeng is surprised at how Quan has cleaned it up. When Quan talks about how failed he is in life, Xiaomeng feels ashamed and tries to encourage him but leaves when he awkwardly lashes out at a loud neighbor.
Xiaomeng later meets with Quan's employer, Wang Yanhui and Yan Sheng, both of whom never met Quan in person. Xiaomeng is shown a video of Quan killing Wu Yanzhen which was actually filmed by Sheng and this is when Xiaomeng learns Quan's true identity as a hitman. Xiaomeng manages to hide his fear and Wang gives him another job to kill Zeng Jiurong for CN¥100,000. When Xiaomeng leaves, he finds a bloodied raincoat and knife in the trunk of Quan's car and becomes terrified and flees for his life but calms down when he realizes he survived suicide once. He later finds Jiurong and gets close to her. As he gets to know her, he backs off from killing her so Wang threatens him.
Xiang meets up with Quan for dinner and secretly records their conversation as she is working on a new project on an amnesiac man. Xiang leaves some words of encouragement on Quan's notepad while also telling him about her own life as a single mother. Quan works hard to practice his acting techniques from watching different films and his serious work ethics wins the praise of directors. Xiang then asks Quan to help her steal an astronaut costume from the film set of The Wandering Earth to pose as You's astronaut father when he performs his speech at school and Quan agrees to help her and her son's speech wins the appauld from the entire school. At night, Quan and Xiang celebrate while pouring out their hearts to each other and after drinking red wine, Xiang expresses her love for Quan and kisses him. Later, Xiang drives Quan to a film shoot and while she watches him in action, a sudden flash during the filming of a killing scene brings Quan's memory back and he leaves the set without Xiang.
Meanwhile, Xiaomeng finds more cash in Quan's apartment which he gives to Jiurong and warns her about being an assassination target and tells her to flee with the cash. Xiaomeng then goes to return Quan's identity to him but is stopped by You who was returning Quan's notebook. At this time, Wang also notices Xiaomeng as an extra in a television series she was watching so she sends her underlings to find him. When Xiaomeng leaves driving Quan's car, Quan suddenly pops out from the back seat and holds a knife to Xiaomeng, demanding him to drive back to his apartment, while unbeknownst to them, Wang's underlings are tailing. Seeing how Xiaomeng has messed up his apartment, Quan slaps him and Xiaomeng attempts to shoot Quan with the latter's pistol which turns out to be an airsoft. Quan berates Xiaomeng and tells him he got cheated by Jiurong, who was pretending to be pregnant. Quan then reveals that he is not a real hitman, but he actually collaborates with his victims to fake their deaths when he receives a hit so he can receive pay from both his employer and his victims. At this time, Wang's underlings arrive at Quan's apartment, so Quan and Xiaomeng escape through a bathtub. Quan then rehearses with Xiaomeng to fake the latter's killing to keep Xiaomeng safe from Wang.
Xiang later calls Quan telling You has gone missing so Quan and Xiaomeng set out to find him and Xiaomeng sees You abducted by Wang's underling. Quan then arrives at Wang's hotpot restaurant posing as an interpol officer to scare Wang into handing out You, but it is foiled when fellow extra actor Ma Ming suddenly barges in their VIP room while drunk. Wang's underlings then beat up Quan and puts him in a bag. Xiaomeng then calls Wang to meet at an abandoned theatre stage and acts pysco and presents her with Jiurong's body and scares her into releasing Quan from the bag. Wang inspects the dead body and realizes the lack of smell of blood and it turns out Xiang disguising as Jiurong. Xiang then suddenly receives a call from You that he is home safe (since Wang's underling was a coward) and Quan reveals to Wang that he is the true Mr. Z and holds Yan hostage with a knife. Quan tells Xiaomeng and Xiang to drive away while he stays behind and is beaten by Wang's underlings. Xiaomeng later runs back to help Quan and the two fight off Wang's underlings before Xiang also comes back when she realizes You has called the police for her. Wang then picks up Quan's knife and stabs him multiple times, but the knife turns out to be fake and the police arrive to the scene.
While both are recovering at the hospital, Quan gifts Xiaomeng his watch as a souvenir. Some time later, Xiaomeng shows up at her ex-girlfriend's wedding begging her to give him back the cash he gave her earlier. Quan is later sentenced to probation for fraud and identification forgery while Wang is sentenced to ten years imprisonment for assault and Wu Yanzhen and Zeng Jiurong are wanted for fraud. When Quan was released from the detention center, Xiang picks him up and hugs him.
