Quartet follows the lives of four musicians—Maki Maki, Sebasu Tsukasa, Bessho Tsukasa, and Sera Mitsukasa—who happen to meet by chance at a karaoke bar in Karuizawa. They decide to form a string quartet and spend the winter living together in a villa. However, this meeting was not as coincidental as it seemed, as each member harbors their own secrets and hidden agendas. As they practice and perform together, the group navigates complex interpersonal dynamics, personal failures, and the weight of their pasts. The series is renowned for its witty, fast-paced dialogue, intricate mystery elements, and its exploration of the bittersweet reality of adulthood, where dreams and reality often collide in unexpected ways.