Fund manager Seok-woo is a cynical workaholic and divorced father. His little daughter Su-an wants to spend her birthday with her mother in Busan. Seok-woo sees a video of Su-an attempting to sing "Aloha ʻOe" at her singing recital and succumbing to stage fright as a result of his absence. Overcome with guilt, he decides to indulge Su-an's wish. They board the KTX 101 at Seoul Station, en route to Busan. Other passengers include working-class man Sang-hwa and his pregnant wife Seong-kyeong, selfish COO Yon-suk, a high school baseball team, including Yong-guk and his cheerleader girlfriend Jin-hee, elderly sisters In-gil and Jong-gil, and a homeless stowaway. As the train departs, an infected woman boards, becomes a zombie and attacks a train attendant. The infection spreads...