A bus bound for a remote wetland carries a quiet mix of passengers: the driver Qiu Chun-sheng, the spoiled runaway Wang Ting, the businessman Liao Tsi-hui, and university student Lin Zi-ping. The journey ends in catastrophe when the bus crashes and explodes, annihilating everyone onboard.
In an interrogation room, the surviving investigators, including Dr. Shen and Detective Wang, reveal a chilling twist: the passengers are not really gone. Their consciousnesses have been implanted into a single body — Subject 193 — which originally belonged to the death-row inmate Chen Kuang-hsuan. A serial killer who preyed on children with disabilities was last seen heading toward the wetlands, and the police suspect one of the bus passengers might be the culprit. Shen and Wang attempt to awaken the various personas inside 193, but Lin Zi-ping’s presence remains nonresponsive, leaving the detectives to conclude that Lin may have died before his consciousness could transmit. The fifth passenger, Hsu Ming-ze, then takes control of the body and quickly reveals his personal longing — he desperately wants to see his daughter — and shares vivid memories of the abducted children that seem to belong to one of the other personas. This makes Shen and Wang curious allies, as Hsu appears cooperative and offers potentially valuable leads.
Inside 193’s mind, the investigation twists and turns as a complex gang of personas confronts the truth. Liao invites Hsu to join the others and escape, while Wang probes deeper into the fractured memories, discovering that Hsu’s daughter died years ago. Seeing an opportunity, Wang chooses to conceal the truth and manipulate Hsu to gain crucial information. Qiu seizes back control of 193’s body, evades surveillance, and triggers an emergency alarm. Shen races to intervene, but she is taken hostage as a high-stakes chase unfolds. The struggle within 193 becomes audible as the different personas fight for supremacy, and the car chase ends with Ting inadvertently taking the wheel. Shen initially escapes, but the lure of a memory about saving a daughter pulls her back, only to be knocked unconscious when the truth about the manipulations is revealed.
When Shen awakens, she finds herself in a junkyard where 193 sits bound and interrogated by a gang. 193 claims to be Liao, and the thug leader, misled by this claim, pays out a bag of money. But the moment 193 kills the thugs in brutal fashion, Shen is horrified and flees, only to be recaptured. 193 insists on being Liao, and through the thugs’ conversations, Shen pieces together that Qiu, Liao, and Ting were all involved in the abductions as the money launderer, getaway driver, and abductor. Wang tracks 193 and Shen to the junkyard, where surveillance footage shows 193 killing with his left hand — a detail that conflicts with the other known personas, pointing towards Lin Zi-ping as the true mastermind. He calls Shen to relay his findings as he and his team close in on Lin’s house to rescue any remaining victims. Meanwhile, Shen and 193 flee to a motel, and Hsu proposes that he can re-enter 193’s mind to uncover Lin’s memories if Shen will look after his daughter.
At Lin’s house, Wang discovers photos of Lin with a prosthetic arm, a clue that Lin cannot be the killer after all. A returning Hsu in 193’s mind witnesses Qiu, Liao, and Ting being slaughtered. Escaping, Hsu encounters a bound Lin, who insists that the real murderer is Hsu Ming-ze, a man who invited everyone onto the bus with plans to kill them all. As the confrontation escalates, a man steps forward and snaps Lin’s neck, revealing himself to be Hsu. In a revealing twist, the Hsu who believed himself to be Hsu is actually Chen Kuang-hsuan, the owner of the body, whose memories are fragmented from brain injuries.
The chase reaches its emotional peak when Wang brings Chen Kuang-hsuan’s daughter to meet 193 and fulfill a promise. 193 makes a disturbing move, attempting to seize the daughter in a hug, and Shen quickly realizes that this is Hsu’s manipulation, not a simple parental gesture. The police subdue 193, and the true Chen Kuang-hsuan’s persona regains control. Chen gently embraces his daughter one final time, and Shen is allowed to execute him, bringing a definitive end to the killer and ensuring that the danger has passed. The case closes with an uneasy quiet — a mind’s labyrinth resolved, leaving behind the memory of lives altered by a body that housed more than one soul.
