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The police receive a phone call, warning them of a bomb on Bus No. 45 that was about to cross the bridge. However, the bomb explodes before they could send help. Li Shi Qing, the one who had informed the police, wakes up in the bus from the dream. She desperately accuses her seat mate, Xiao He Yun, of being a pervert and successfully manages to get off the bus with him. They part on unfriendly terms and the boy soon gets into a taxi that stops behind the bus. The bus once again explodes, severely injuring everyone on sight. A shocked Li Shi Qing is struck by a bike and she falls unconscious. Waking up in the hospital, she is questioned by Chief Zhang and his colleagues, who had captured footage of her and He Yun getting off the bus. While explaining the events, Shi Qing realizes that she had been experiencing the event over and over again. Chief Zhang, although sceptical, calls this a "bus loop". Xiao He Yun succumbs to his injuries. He wakes up in Bus No. 45.

Xiao He Yun wakes up in the bus, entering the Time Loop. He experiences the explosion twice before realizing that it wasn't a dream. He recognizes Li Shi Qing, who had once again entered the loop. He Yun attempts several tricks in order to escape. Both of them manage to successfully divert the collision that would lead to the bomb exploding. However, they realize that the bomb was purposefully being detonated from within the bus. Shi Qing and He Yun get off and inform the police about the coming explosion. He asks her to switch off her phone. The bus explodes just as she had predicted, convincing the police that it wasn't a lie. Li Shi Qing and Xiao He Yun have a talk. The police begin to track them.

Xiao He Yun and Li Shi Qing create a detailed timeline of the events to find clues about the explosion. They learn that each time they return to the loop they wake up one minute earlier than before. They can't agree about what to say to the police. The police find them and take them in for questioning. They both tell the police about the loop, but the police don't believe them.

Li Shi Qing wakes up on the bus again after falling asleep. Xiao He Yun says there is a bomb on the bus and when they announce there is a bomb on the bus, the bus explodes. They determine that the bomber is riding the bus with them. They decide that the rider in the back seat is the bomber and try to find out if the bomb is in his backpack. Xiao He Yun tries to get out of the loop when they manage to leave the bus at the next stop. However the bus still explodes and kills some police officers as well. Li Shi Qing says she doesn't know Xiao He Yun, but he calls her while she is being interrogated.

Li Shi Qing pretends that Xiao He Yun is her ex-boyfriend. The police search for Xiao He Yun and he tries his best to fall asleep and return to the beginning of the loop. This time they decide not to call the police and to investigate the bomber on their own. They start with the man in the last seat. They find out that Lu Di isn't the bomber.

The police confirm residues of a bomb on the bus. They decide to further investigate everyone who had entered Bus. 45. The masked man takes He Yun and Li Shi Qing to his secret apartment where he raises cats. He believes their story and they part amicably. Still unsure about whether he would enter the loop or not, he asks the two of them to address him by his name "Lu Di" the next time they meet. Li Shi Qing and Xiao He Yun stay at a hotel room and surf the web for information about anymore passengers. Back at his home, Lu Di and his mother argue over him keeping cats as he was highly asthmatic. He shuts himself in his rooms and pens a heartfelt final letter to his parents before he is summoned by the police. Li Shi Qing and Xiao He Yun receive calls from the police soon. They speculate about how the events are going to turn out and what Lu Di would've told. The police question Lu Di and the other two arrive at the station. 

Li Shi Qing and Xiao He Yun go in to talk to the police and lie about why they stopped Lu Di from getting on the bus. They tell the police about suspicious people on the bus. They start investigating Ma Guo Qiang and Li Shi Qing stays to learn more clues. Lu Di's diary is brought to the police station and they learn that Li Shi Qing and Xiao He Yun know about the explosion. Getting back into the loop they decide to investigate Ma Guo Qiang and his bag. Lu Di did not enter the loop.

Lao Jiao, a struggling construction worker works hard to make ends meet and provide for his daughter in high school. He is asked to leave the garage that he was renting by the owner as the Fire Department had begun issuing fines to such tenants. Back in the time loop, Xiao He Yun and Li Shi Qing decide to investigate the two remaining passengers -- a lady with a red plastic cover and Lao Jiao. Shi Qing approaches the lady in the guise of asking for sanitary pads, but her unflinching attitude removes their doubts about her. Lao Jiao, who had them in his suitcase, opens and offers the pads to Shi Qing, proving his innocence. He Yun approaches the lady with the cover to confirm their suspicion; she pulls a plug and explodes the bomb. Once again back in the time loop, Shi Qing and He Yun decides to attempt to save the passengers. They are fatally stabbed by the lady, who then proceeds to detonate the bomb. The time loop begins again and Shi Qing attempts to snatch the red cover for the last time. The lady tries to stab her, but He Yun blocks her. A brief scuffle follows and he stabs the lady. Dazed, bloodied and shocked, he leaves the bus with Shi Qing. It explodes behind them. 

The police start investigating the explosion with Xiao He Yun and Li Shi Qing as the prime suspects. Li Shi Qing refuses to leave a traumatized He Yun and they attempt to evade the police together. While seeking information about Jiang Xiangrong from Gangwu New Village, the police learn about Tao Ying Hong, the lady with the red cover, who had been a tenant in the building and had once had an explosion in her garage. Shi Qing and He Yun escape to Lu Di's apartment in Anime Park to take care of He Yun's wounds while the police follow close at their heels.

The police track Li Shi Qing and Xiao He Yun to his friend's place. His friend convinces him to surrender to the police. They return to the bus and try to save everyone, but the bomb explodes. Once again back in the loop, He Yun and Shi Qing manage to finally get assistance from two other passengers, but realizes that the bomber has an accomplice after the driver refuses to stop the bus. 

Xiao He Yun and Li Shi Qing get off the bus before it explodes to investigate the bus driver. They go to the police to give them clues and hopefully get more clues. However the police are suspicious of their intentions.

The police find out that Li Shi Qing and Xiao He Yun were investigating the bus driver. The police find out the motive for the explosion and the result is fast. They keep wondering about the source of information and their motive. Li Shi Qing asks the police officer how to stop a bomb on the bus. This time they get the police involved immediately, however the bus doesn't stop. 

We learn what happened five years ago. Zhang Cheng is seriously injured in the blast and dies. They think there is something else missing from the loop. 

Wang Xing De's wife makes him feel guilty about not answering his daughter's phone call. Wang Xing De gets hired to drive a bus and he wants to drive route 45. His wife creates a bomb. Li Shi Qing tries to find out what happened to Wang Xing De's daughter. They find a witness to the accident five years ago.

We finally learn the real reason Wang Xing De's daughter died. They even have a photo of the culprit. This time Li Shi Qing puts the plan in action because Xiao He Yun doesn't wake up. They end up stopping the bomb with zero casualties.