Do Ki is a young man who lived more honestly than anyone else as a special forces officer. But when his mother is killed by a serial killer, he spends his days in despair. Feeling betrayed and broken, Do Ki meets Jang Sung Chul, who hires him at his company, Rainbow Taxi. Far from being an ordinary taxi service, Rainbow Taxi is a secret organization that avenges victims whom the law has failed to protect. Do Ki becomes a renowned driver who carries out satisfying acts of revenge. Meanwhile, Ha Na is a prosecutor investigating Rainbow Taxi. She is furious at their illegal activities but at the same time feels a sense of admiration seeing them resolve cases that the law cannot reach. Caught between those who believe revenge represents true justice and those who prosecute criminals, Do Ki searches for the true meaning of justice.