You cannot discuss Secret Love Affair without praising and Yoo Ah-in . Kim Hee-ae delivers the performance of her career as Hye-won. She conveys decades of exhaustion and longing with just a flicker of her eye. Yoo Ah-in, meanwhile, is volcanic. He plays Sun-jae as a bundle of raw nerves and unbridled talent. Their chemistry is palpable; a single piano duet (Liszt’s Piano Concerto No. 1 ) is more erotic than most explicit sex scenes in Western television.