On the surface, she is a prim, ascetic university lecturer × he is a chaebol board member and student retaking her elective course. In reality, they are old lovers from five years ago in the Nevada desert—a story of “the older sister and the stray cat” and redemption. To win her back, the male lead dyes his hair deep-sea diamond blue and builds a seaside cliff manor; the female lead is his one and only obsession. Taboos: a five-year age gap, a teacher-student relationship, and the identities of board member and lecturer. Secrets: that midsummer five years ago, the truth behind the blue hair, a wall covered with photos of the wasteland, and silver cross earrings.