26-year-old Yong-jun hasn't quite figured things out yet – but when he reluctantly agrees to start working part-time for his parents' lunchbox shop, a chance encounter suddenly breathes new life and possibility into his summer. Making a delivery to a swimming pool, he meets and immediately falls for Yeo-reum: the sunny and devoted sister to Ga-eul, a gifted swimmer who is deaf and training to qualify for the Olympics. The two sisters communicate in Korean Sign Language, which Yong-jun is fluent in too. Chasing his heart, Yong-jun sparks a journey of discovery in all three of their lives.