Despite the disbandment of Rainbow Taxi, Do-ki is still out there going after bad guys. While keeping it from the rest of the members, Do-ki and Sung-cheol secretly help out a father who is searching for his missing son. To confirm his whereabouts, Do-ki sets off abroad to a foreign country to accomplish his first mission.

Do-ki successfully infiltrates Cheongeum with the help of his old crew. He pretends to be an abducted recruit but secretly searches for Dong-jae. During the search, he runs into Lim Bok-ja. He uses her revengeful anger to make it easier to find the missing boy. Just when he is about to capture the mastermind, a mysterious gun shot interrupts his arrest.

An elderly woman visits Rainbow Transport as a victim. She owes a lot of money because of a young scammer who only rips money off old people. Do-ki and the team get infuriated upon seeing this and set up a plan to prevent this criminal from ever scamming the elderly again.

Rainbow Transport officially begins its operation to bring punishment to Sang-gi. The plan mainly depends on Sung-cheol being a loaded old man as bait. As soon as Sang-gi sees this and plans to scam him, he does not realize the karma that he is about to face. Meanwhile, the secret organization Do-ki is after is also keeping an eye on Do-ki as well.

Do-ki runs into a stray little girl on the street. Out of concern, he takes her to Rainbow Transport and learns that suspicious people are after her. Do-ki and the team tries to infiltrate Feel Consulting and get some info on Kang Pil-seung to find out why he is in search of this poor little girl.

Do-ki and Go-eun get busted by Pil-seung for putting up an act. However, Do-ki manages to win back his trust by acting how desperate he is for a house. Now that they are back on track, Do-ki learns how Pil-seung is able to help couples get housing by using children. Disgusted by his ways, the team is determined to bring down Pil-seung at all costs.

The next client is a woman named Lee Jin-hee. Her beloved sister Jin-sun is suffering from a terminal disease and is relying on a cult to cure her. To save her from the cult and to take down its leader, Rainbow Transport begins service. However, Do-ki is not the one who will be infiltrating the cult this time.

A smelly drunk man protests alone in front of a big hospital. He claims that his daughter is in a coma due to a surgery malpractice. Although Rainbow Transport took him in as a client, they are not sure whether this is an actual case or just an accident. Before they start anything, Do-ki looks into Ahn Young-sook, the director who performed the surgery.

Do-ki becomes a patient himself to infiltrate the operating room. When he is put to sleep, Go-eun finds out that there is a proxy who does the actual surgery while Young-sook goes somewhere else for a drink. Now that the team knows she is a complete fraud, they set up a meticulous plan to bring the witch down.

Do-ki makes it out alive from the car bomb explosion. He uses his death to track down the person behind the vicious attack. While his funeral progresses, Do-ki and the team monitor any suspicious people coming and going, which leads them to a club for the rich in Gangnam. Do-ki makes his entrance to find out more.

After Do-ki gets kicked out from Black Sun and gets beaten up, the police arrive. However, the police arrest Do-ki instead. Although Yong-min helps him to bail out, Do-ki now knows that the police are working with Black Sun. Rainbow Transport infiltrates the club to take them down for all the crimes they are committing.

An angry VIP client at Black Sun puts the security team on edge. The security team gets a second chance to make another delivery. Only this time, Do-ki joins the team. What he learns is shocking. Meanwhile, Sung-cheol digs into Ha-joon's past.

While Do-ki wakes up from getting drugged, the bishop comes back to Korea. Now that Do-ki has evidence of how Black Sun is circulating drugs, he sets up a plan. Meanwhile, Ha-joon notices that Rainbow Transport is on Black Sun’s tail. Knowing how skillful Do-ki is, he takes every precaution he can take.

Rainbow Transport takes in another client. However this time, it is a set-up made by the Bishop and Ha-joon. Not knowing that it is a trap, Do-ki blindly goes into Jangsan Correctional with Kyung-goo and Jin-eon to save a victim. The only thing that is waiting for him is Ha-joon's trap that will break Do-ki into pieces.

Do-ki goes into Jangsan Correctional as an undercover inmate. He fights all the way through every trap that Ha-joon has prepared for him. Although he barely makes it in one piece, he saves Lee Si-wan. Meanwhile, Ha-joon learns about his true identity and what the Bishop has done to him since his childhood.