Hyunsun, after leading an exceptionally ordinary life, embraces the milestone of turning 40—an age often viewed as the threshold of wisdom, where one is expected to stop drifting and start making meaningful choices. Wishing to start something new before it’s too late, he enrolls in guitar school. There, he encounters the young instructor, Yeoreum (T/N: 'Summer' in Korean), and for the first time, he feels a stirring passion for life. Their connection deepens, igniting a sense of purpose he thought he’d lost. But of course, the world is always full of unexpected turns. As Yeoreum starts to show Hyunsun his wholesome and charming affection, their relationship faces a new situation…