Se-oh (Han Hyun-min) works at an amusement park as a white-tiger-costumed mascot and collapses one day due to overwork. He then makes a resolution with himself — buys a luxury suitcase and goes travelling. He gets on the subway and finds So-ra (Lee Zoo-young) appears at his side. The Mutation explores their journey and gradually explores the facets of their pasts as well: Se-oh, who is of Black, mixed-race descent but knows little about the circumstances of his birth, feels that it is safer for him to live in society wearing a mask, while So-ra has lived under shadows following the death of her same-sex lover. Rather than portraying a grand moment of salvation, the film shines light on the simple but powerful gesture of reaching a hand out to someone who has fallen.