The fifth episode of Season 3 of Taxi Driver opens with the Rainbow Taxi team spending a day with their friend Maria, the director of the Bluebird Foundation for orphaned children. They play with the kids, share a meal, and experience pure joy. Do-gi catches a glimpse of a sprain bandage on Sung-chul's wrist and insists he visit the hospital.
At the hospital, Sung-chul receives a call from his old friend, Park Dong-su. The elderly man requests Sung-chul's presence to see Dong-hyeon, who is being released from prison that day. Sung-chul makes his way to the prison but finds it empty of any sign of Dong-hyeon's presence.
Later, Kyung-koo and Jin-eon introduce Go-eun to a new spy camera installed in the taxi. Sung-chul then contacts Go-eun to track the phone number Dong-su used to call him. She locates the phone booth and notes that there is a nursing home nearby. Sung-chul visits and finds Dong-su, who does not recognize him. A nurse explains that Dong-su has developed Alzheimer's after a severe car accident. Sung-chul pays his medical expenses and collects his belongings, discovering a journal that reveals the lowest moment of his life was when his son Min-ho disappeared.
The rest of the Rainbow Taxi crew is worried as Sung-chul suddenly leaves the hospital. Eventually, they find him at a restaurant, drinking alone. They urge him to share what is troubling him, and Sung-chul finally reveals that Dong-su is the reason he created Rainbow Taxi. A flashback shows a younger Sung-chul in court, where he meets Dong-su, furious about the lenient punishment given to Dong-hyeon, the suspect in Min-ho's disappearance and murder. The court only gave Dong-hyeon five months for assault, without charging him for murder. Sung-chul understands Dong-su's rage as he too feels betrayed by the law.
One day, Dong-su tried to end his life by jumping into the river, but Sung-chul stopped him. He vowed to seek the truth behind Min-ho's disappearance, investigating together by questioning Min-ho's friends and fellow basketball players.
As the bond between the two men deepened, Sung-chul's relentless pursuit of the case led him to the law firm representing Dong-hyeon. He demanded access to the CCTV footage shown in court but not included in the files, and the lawyer eventually relented, handing over the recording. The footage revealed Dong-hyeon and Min-ho in the locker room with a third, unseen figure outside the frame. The unknown figure attacked Min-ho, who left the locker room injured.
Dong-su attempted to meet Dong-hyeon in prison, begging him to reveal the identity of the third person, but Dong-hyeon remained stubbornly silent. Frustrated, Dong-su announced that he would no longer pursue the truth. Sung-chul promised to meet him outside the prison upon Dong-hyeon's release, to tell him about his new business venture, Rainbow Taxi.
However, on the day of release, Dong-su failed to show up. Sung-chul visited his house and found it sold, with no sign of Dong-su anywhere. In the present, Sung-chul tells the Rainbow Taxi crew that after all these years, Dong-su does not even remember him anymore. Do-gi insists that they need to uncover the truth before Dong-su loses all remaining memories.
The team embarks on their investigation, with Go-eun reviewing documents while Do-gi, Kyung-koo, and Jin-eon sift through Dong-su's old belongings for clues. That night, Do-gi and Go-eun reflect on how this time Sung-chul has become their client, making the case deeply personal.
One night, Dong-su dreams of Min-ho calling for help. He wanders outside the nursing home and nearly gets run over by a car. Sung-chul is there to save him just in time. The other members review CCTV footage and see that Min-ho walked out of the practice court on his own the night he died.
They try to figure out who Dong-hyeon is protecting and go to the gym. There, they witness Dong-hyeon leave with a bag full of cash and take Do-gi's taxi. Do-gi drops him off at a funeral home but is blocked when he tries to enter. Using an antenna spy camera, they peek through a window and discover a gambling den hidden within the funeral home. Go-eun explains that Dong-hyeon is deeply in debt due to his addiction. Do-gi decides to pressure him by pretending to be Min-ho and sending threatening messages. The calls and letters terrify Dong-hyeon, who rushes to meet his old friend, Jo Seong-uk.
Do-gi follows and overhears their conversation. Dong-hyeon admits he received messages from Min-ho and asks Seong-uk if he buried Min-ho as he promised. Do-gi immediately calls Sung-chul to inform him about Seong-uk's involvement.
The episode ends with Dong-su waking from another dream and regaining his memories for a brief moment. He sees Sung-chul beside him, and Sung-chul vows to uncover the truth behind Min-ho's disappearance and murder.
